Wireless base station device, terminal, and wireless communication method

ABSTRACT

A wireless base station device includes a plurality of transmit weight generation sections and a beam selection section. The transmit weight generation sections generate pieces of transmit weight information used for spatial division multiplexing transmission according to different algorithms. The pieces of transmit weight information are generated based on channel information on a plurality of terminals each having one or more antennas with which the wireless base station device performs spatial division multiplexing transmission. The beam selection section selects one of the pieces of transmit weight information generated.

This application is a divisional of U.S. patent application Ser. No.11/911,165, filed Oct. 10, 2007, which is a U.S. National PhaseApplication of PCT International Application PCT/JP2006/307613, which isincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a wireless base station device whichperforms spatial division multiplexing transmission with terminals; tothe terminals which support spatial division multiplexing transmission;and to a method of wireless communication between the wireless basestation device and the terminals.

BACKGROUND ART

In recent years, wireless communication has been increasingly requiredto have higher capacity and higher speed, so that it has been activelystudied to further improve utilization efficiency of finite frequencyresources. Of the various methods developed so far, the use of thespatial domain is drawing attention.

One of the spatial domain techniques is to use adaptive array antennas(adaptive antennas). In this technique, a received signal is multipliedby a weighting coefficient to adjust its amplitude and phase. Thisallows to strongly receive a signal that is intended to be received(hereinafter, a “desired signal”) and to suppress the interferencesignal, thereby reducing co-channel interference and increasing systemcapacity.

Another of the spatial domain techniques is to use spatial orthogonalityin a propagation path. In the technique, different data sequences aretransmitted to different terminals using physical channels having thesame time, the same frequency, and the same sign.

Spatial division multiplexing transmission technology is described, forexample, in non-patent document 1 (T. Ohgane et al, “A study on achannel allocation scheme with an adaptive array in SDMA”, IEEE 47thVTC, pages 725-729, vol. 2, 1997). A wireless base station device andterminals for spatial division multiplexing transmission based on thistechnology can perform spatial division multiplexing transmission if thespatial correlation coefficient between the terminals is lower than apredetermined value. This improves the throughput of the radiocommunication system and the concurrent user capacity.

However, in such a conventional structure, the wireless base stationdevice is required to detect a spatial correlation coefficient betweenthe terminals and to select the terminals having a spatial correlationcoefficient smaller than the predetermined value as the terminals to beconnected by spatial division multiplexing (hereinafter, this selectingoperation is referred to as “allocation”).

Furthermore, the spatial correlation coefficient is required to bedetected and updated frequently or periodically because it has thenature of varying with time due to changes in the propagationenvironment associated with the movement of the terminals or surroundingobjects. This complicates both the detection of a spatial correlationcoefficient and the allocation of the terminals to be connected byspatial division multiplexing, thereby increasing the processing delayassociated therewith.

SUMMARY OF THE INVENTION

The wireless base station device of the present invention includestransmit weight generation sections; a beam selection section; and atransmit beam formation section. The transmit weight generation sectionsgenerate transmit weight information according to different algorithmsand based on the channel information on a plurality of terminals withwhich the wireless base station device performs spatial divisionmultiplexing transmission. The transmit weight information is used toform transmit beams to be transmitted to the plurality of terminals. Thebeam selection section selects one of pieces of transmit weightinformation generated according to the different algorithms. Thetransmit beam formation section forms the transmit beams using theselected transmit weight information.

This structure allows to select an optimum transmit weight from amongthose generated according to different transmit weight generationalgorithms. The optimum transmit weight is optimum for the spatialcorrelation conditions between the terminals detected by the channelinformation at the time of spatial division multiplexing transmission tothe terminals. This achieves spatial division multiplexing transmissionrobust to the spatial correlation conditions between the terminals,thereby simplifying the conventional allocation process based on thespatial correlation coefficient. As a result, the wireless base stationdevice can be simplified and the processing time required to control thespatial division multiplexing transmission can be reduced. Thus, thewireless base station device, the terminal, and the wirelesscommunication method of the present invention can increase the systemcapacity by spatial division multiplexing transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a wireless base station device and terminalsaccording to a first embodiment of the present invention.

FIG. 2A is a detailed diagram showing a terminal having a plurality ofreceiving unit antennas according to the first embodiment of the presentinvention.

FIG. 2B is a detailed diagram showing a terminal having one receivingunit antenna according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing the operation to perform spatial divisionmultiplexing transmission according to the first embodiment of thepresent invention.

FIG. 4A shows an antenna element arrangement of a wireless base stationantenna which is used in a simulation of the relationship between acorrelation coefficient and communication quality in three differentalgorithms according to the first embodiment of the present invention.FIG. 4B shows an antenna element arrangement of a receiving unit antennawhich is used in the simulation of the relationship between thecorrelation coefficient and communication quality in the three differentalgorithms according to the first embodiment of the present invention.

FIG. 4C is a model diagram showing radio propagation between a wirelessbase station antenna and a receiving unit antenna which are used in thesimulation of the relationship between the correlation coefficient andcommunication quality in the three different algorithms according to thefirst embodiment of the present invention.

FIG. 4D is a model diagram showing a beam width on a transmitting side,which is used in the simulation of the relationship between thecorrelation coefficient and communication quality in the three differentalgorithms according to the first embodiment of the present invention.

FIG. 4E is a model diagram showing a beam width on a receiving side,which is used in the simulation of the relationship between thecorrelation coefficient and communication quality in the three differentalgorithms according to the first embodiment of the present invention.

FIG. 5 is a diagram showing simulation conditions according to the firstembodiment of the present invention.

FIG. 6 is a graph showing simulation results of the relationship betweenthe correlation coefficient and communication quality in the threedifferent algorithms when Ricean factor K=3 dB according to the firstembodiment of the present invention.

FIG. 7 is a graph showing simulation results of the relationship betweenthe correlation coefficient and communication quality in the threedifferent algorithms when Ricean factor K=6 dB according to the firstembodiment of the present invention.

FIG. 8 is a graph showing simulation results of the relationship betweenthe correlation coefficient and communication quality in the threedifferent algorithms when Ricean factor K=9 dB according to the firstembodiment of the present invention.

FIG. 9A is a diagram showing the spatial division multiplexingtransmission of a first transmission data frame sequence along thetemporal and spatial axes according to the first embodiment of thepresent invention.

FIG. 9B is a diagram showing a structure of the first transmission dataframe sequence according to the first embodiment of the presentinvention.

FIG. 10A is a diagram showing the spatial division multiplexingtransmission of a second transmission data frame sequence along thetemporal and spatial axes according to the first embodiment of thepresent invention.

FIG. 10B is a diagram showing a structure of the second transmissiondata frame sequence according to the first embodiment of the presentinvention.

FIG. 11 is a diagram showing a wireless base station device andterminals according to a second embodiment of the present invention.

FIG. 12 is a diagram showing a wireless base station device according toa third embodiment of the present invention.

FIG. 13 is a diagram showing a terminal according to the thirdembodiment of the present invention.

FIG. 14 is a diagram showing a wireless base station device according toa fourth embodiment of the present invention.

FIG. 15 is a diagram showing a terminal according to the fourthembodiment of the present invention.

FIG. 16 is a diagram showing another terminal according to the fourthembodiment of the present invention.

REFERENCE MARKS IN THE DRAWINGS

-   -   1, 100 wireless base station device    -   2-1, 2-2, 2-s, 2-A, 2-B terminal    -   3-1, 3-2, 3-s transmission signal generation section    -   4 channel information acquisition section    -   5 transmit weight determination section    -   6-1, 6-2, 6-n transmit weight generation section    -   7 beam selection section    -   8 transmit power determination section    -   9 transmit beam formation section    -   11-1, 11-2, 11-s, 60 wireless base station antenna    -   20-1, 20-m, 62 receiving unit antenna    -   107-a, 107-b selector switch section    -   216 transmitting unit antenna    -   221-1, 221-m reception section    -   222 channel estimation section    -   223 spatial division demultiplexing section    -   224 demodulation section

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A wireless base station device and terminals of each embodiment of thepresent invention are described with reference to drawings.

Note that in the following description, a plurality of sections, aplurality of units, a plurality of terminals, or the like having thesame structure are referred to with a single reference number when it isunnecessary to distinguish between them. On the other hand, when it isnecessary to distinguish between them, they are referred to with thereference number and another reference number or symbol with a hyphenbetween them. For example, a plurality of terminals having the samestructure may be referred to as “terminals 2” when it is unnecessary todistinguish between them and referred to as “terminals 2-1, 2-2, and2-s” when it is necessary to distinguish between them.

First Embodiment

The structure of a wireless base station device and terminals of a firstembodiment of the present invention is shown in FIG. 1. In FIG. 1,terminals 2-1 to 2-s each have antennas 20-1 to 20-j, 20-1 to 20-k, and20-1 to 20-s, respectively, but may each have only one antenna. FIGS. 2Aand 2B show detailed diagrams of a terminal having a plurality ofantennas and a terminal having a single antenna, respectively, on thereceiving side.

FIG. 1 is a diagram of wireless base station device 1 and terminals 2-1to 2-s according to the first embodiment of the present invention. Thefollowing description of the present embodiment assumes a case wherewireless base station device 1 transmits “Ns” spatial streams to “s”terminals where Ns≧s and Ns is a natural number. The transmission fromwireless base station device 1 to terminals 2-1 to 2-s is hereinafterreferred to as “downlink”.

In FIG. 1, wireless base station device 1 of the first embodiment of thepresent invention includes transmission signal generation sections 3-1to 3-s; channel information acquisition section 4; transmit weightdetermination section 5; transmit power determination section 8;transmit beam formation section 9; power factor multipliers 10-1 to10-s; and wireless base station antennas 11-1 to 11-s. Transmissionsignal generation sections 3-1 to 3-s generate transmission datasequences to be transmitted to terminals 2-1 to 2-s, respectively, withwhich wireless base station device 1 performs spatial divisionmultiplexing transmission. Channel information acquisition section 4extracts channel information of the downlink from signals received fromterminals 2-1 to 2-s. Transmit weight determination section 5, whichdetermines a transmit weight, has transmit weight generation sections6-1 to 6-n and beam selection section 7. Transmit weight generationsections 6-1 to 6-n generate pieces of transmit weight informationaccording to different generation algorithms. Beam selection section 7selects an optimum one of the pieces of transmit weight informationgenerated by transmit weight generation sections 6-1 to 6-n. Transmitpower determination section 8 determines the transmit power for eachspatial stream based on the selected transmit weight information andtransmits transmit power control information. Transmit beam formationsection 9 multiplies each transmission data sequence by a transmitweight based on the selected transmit weight information and thenconverts the multiplied signals into radio frequency signals so as toform specific transmit beams. Power factor multipliers 10-1 to 10-smultiply the output signal of each of transmission signal generationsections 3-1 to 3-s by a predetermined power factor based on thetransmit power control information for each spatial stream determined bytransmit power determination section 8. Wireless base station antennas11-1 to 11-s transmit the radio frequency signals received from transmitbeam formation section 9 over an unillustrated transmission medium.

In FIG. 2A, terminal 2-A of the first embodiment of the presentinvention as a terminal having a plurality of antennas on the receivingside includes transmission unit 210 having transmitting unit antenna216, and reception unit 220 having receiving unit antennas 20-1 to 20-m.

Transmission unit 210 includes data input section 214 and transmissionsection 212. Data input section 214 receives data information that theterminal user is going to transmit. Transmission section 212 performspredetermined data processing to channel estimation informationtransmitted from channel estimation section 222 and converts it to aradio frequency signal.

Reception unit 220 includes reception sections 221-1 to 221-m; channelestimation section 222; spatial division demultiplexing section 223;demodulation section 224; and data output section 225. Receptionsections 221-1 to 221-m correspond to receiving unit antennas 20-1 to20-m, respectively, and convert the radio frequency signals received byreceiving unit antennas 20-1 to 20-m into baseband signals. Channelestimation section 222 estimates channel response information ofpropagation paths of the downlink from the baseband signals. Spatialdivision demultiplexing section 223 separates and extracts a desiredsignal from each spatial division multiplexing signal based on thechannel response information obtained by channel estimation section 222.Demodulation section 224 restores the transmission data sequences fromthe separated desired signals. Data output section 225 either outputsthe restored reception data sequences to another apparatus or providesthe information to the terminal user.

Note that transmitting unit antenna 216 and receiving unit antennas 20-1to 20-m are treated as different components; however, alternatively,transmitting unit antenna 216 can be integrated with one of receivingunit antennas 20-1 to 20-m.

In FIG. 2B, terminal 2-B of the first embodiment as a terminal having asingle antenna on the receiving side includes transmission unit 210having transmitting unit antenna 216 and reception unit 230 havingreceiving unit antenna 20-1.

Terminal 2-B differs from terminal 2-A of FIG. 2A in that terminal 2-Bhas only one receiving unit antenna 20-1, so that reception unit 230does not include spatial division demultiplexing section 223 performinginterference cancellation in spatial domain. Transmitting unit antenna216 and receiving unit antenna 20-1 are treated as different components;however, alternatively, these antennas can be integrated together in thesame manner as terminal 2-A.

The following is a description of the operation of wireless base stationdevice 1 and terminal 2-A or 2-B. Assuming that the channel informationof the downlink has been estimated by terminals 2-1 to 2-s, theoperation to provide this information to wireless base station device 1is briefly described.

First, the channel information of a propagation path (unillustrated)estimated by channel estimation section 222 in transmission unit 210 ofterminal 2-A or 2-B is transmitted to transmission section 212 and thentransmitted to wireless base station device 1 via a control channel or abroadcasting control channel. In other words, a control channel signalor a broadcasting control channel signal carrying the channelinformation is transmitted to transmitting unit antenna 216 and thenemitted therefrom to the propagation path (unillustrated) so as to betransmitted to wireless base station device 1.

The control channel or the broadcasting control channel is acommunication channel to exchange information of the efficient operationbetween wireless base station device 1 and terminal 2-A or 2-B and isdifferent from a communication channel to exchange information betweenthe user of terminal 2-A or 2-B and wireless base station device 1.

The information that the user of terminal 2-A or 2-B is going totransmit is transferred from data input section 214 to transmissionsection 212 where the information is subjected to predetermined signalprocessing; converted into a radio frequency signal; and transmitted towireless base station device 1 via transmitting unit antenna 216.

Later, in wireless base station device 1, channel informationacquisition section 4 extracts the channel information contained in thecontrol channel signal or the broadcasting control channel signaltransmitted from each of terminals 2-1 to 2-s to wireless base stationantennas 11-1 to 11-s. Terminals 2-1 to 2-s have the structure ofterminal 2-A or 2-B. Channel information acquisition section 4 thenoutputs the extracted channel information to transmit weightdetermination section 5.

The following is a brief description of the operation of spatialdivision multiplexing transmission by multiplying each of the signals tobe transmitted to terminals 2-1 to 2-s by a predetermined transmitweight. Terminals 2-1 to 2-s are to be connected by spatial divisionmultiplexing (allocated) based on the channel information of thedownlink which has been notified to wireless base station device 1.

First, in wireless base station device 1, channel informationacquisition section 4 extracts the channel information contained in thecontrol channel signal or the broadcasting control channel signaltransmitted to wireless base station antennas 11-1 to 11-s from each ofterminals 2-1 to 2-s to be connected by spatial division multiplexing(allocated). Channel information acquisition section 4 then outputs theextracted channel information to transmit weight determination section5. The channel information thus extracted is the channel information ofthe downlink from wireless base station device 1 to terminals 2-1 to2-s.

Next, in transmit weight determination section 5, transmit weightgeneration sections 6-1 to 6-n, which have different transmit weightgeneration algorithms, generate pieces of transmit weight generationinformation. This allows transmitting an optimum signal to terminals 2-1to 2-s to be connected by spatial division multiplexing in accordancewith the correlation conditions between terminals 2-1 to 2-s. Then, beamselection section 7 selects the transmit weight information thatmaximizes a predetermined criterion from among the pieces of transmitweight generation information generated by first to n-th transmit weightgeneration sections 6-1 to 6-n. Beam selection section 7 then outputsthe selected information to transmit power determination section 8 andto transmit beam formation section 9.

Next, transmit power determination section 8 determines a powerdistribution factor used to determine the transmit power for eachspatial division multiplexing stream, based on the received transmitweight information.

On the other hand, transmission signal generation sections 3-1 to 3-sgenerate signals to be transmitted to terminals 2-1 to 2-s to beconnected by spatial division multiplexing (allocated). The signals tobe transmitted to terminals 2-1 to 2-s (hereinafter, “transmission datasequences”) are outputted after being subjected to predetermined signalprocessing.

Power factor multipliers 10-1 to 10-s multiply the signal output of eachof transmission signal generation sections 3-1 to 3-s by thecorresponding one of the power distribution factors determined bytransmit power determination section 8.

Transmit beam formation section 9 generates baseband symbol data bymultiplying each of transmission data frame sequence signals (describedlater) by a transmit weight used to form a predetermined (selected)beam, based on the transmit weight information from beam selectionsection 7. The transmission data frame sequence signals have beenobtained by the multiplication between the signal outputs and the powerdistribution factors. After this, in transmit beam formation section 9,digital data, which are the baseband symbol data, are digital-analogconverted by an unillustrated digital-analog converter, filtered by anunillustrated band limiting filter, and converted into carrierfrequencies by an unillustrated frequency converter, thereby beingoutputted as radio frequency signals.

Wireless base station antennas 11-1 to 11-s emit the received radiofrequency signals to unillustrated propagation paths (space) so as totransmit these signals to terminals 2-1 to 2-s to be connected byspatial division multiplexing.

How terminals 2-1 to 2-s receive the spatially multiplexed signalstransmitted from wireless base station device 1 will be described later.Before that, the operation flow including scheduling for wireless basestation device 1 to perform spatial division multiplexing transmissionof the downlink is described first, and then the operation and criterionof each step of the flow and weight generation algorithm are describedin detail.

FIG. 3 is a flowchart showing the operation for wireless base stationdevice 1 to perform spatial division multiplexing transmission of thedownlink. The spatial division multiplexing transmission in wirelessbase station device 1 of the downlink is described as follows withreference to FIGS. 1 to 3. To make the explanation easy to understand,the operation is described briefly first and then in detail.

First, among terminals 2-1 to 2-s, not more than s terminals 2-k where sis a natural number and k=1 to s which are to be connected (allocated)preferentially in downlink transmission are selected by predeterminedpacket scheduling (Step S30). Examples of the scheduling include MaximumCIR and Proportional Fairness, which are based on thesignal-to-interference power ratio (hereinafter referred to as “SIR”) asa value indicating the reception quality of the terminals. These twoexamples are disclosed as well-known techniques in A. Jalali et al,“Data Throughput of CDMA-HDR a High Efficiency-High Data Rate PersonalCommunication Wireless System” IEEE VTC 2000-Spring, pp. 1854-1858.

Next, channel information acquisition section 4 acquires the downlinkchannel information on allocated terminals 2-1 to 2-s (Step S31). Thedownlink channel information can be acquired by making terminals 2-1 to2-s feedback the observed channel information in advance to wirelessbase station device 1. In the case of the TDD (Time division duplex)system, the downlink channel information can be acquired by using therelativity of a propagation path and based on the known signal sequencestransmitted from terminals 2-1 to 2-s in the uplink.

In the following description, the channel estimation matrix on k-thterminal 2-k is represented as “H(k)”, which is the channel informationacquired under the assumption of flat fading. Flat fading represents thecircumstance in which fading has a uniform effect on the frequency bandsto be considered, so that there is no need to consider the effect ofmultipath. The channel estimation matrix consists of Nr(k) rows and Ntcolumns. The Nr(k) rows correspond to the number of receiving antennasin k-th terminal 2-k and the Nt columns correspond the number ofwireless base station antennas. The j-th row s-th column element of thechannel estimation matrix represents a complex channel response when thesignal transmitted from the s-th antenna of wireless base station device1 is received by j-th receiving antenna 20-j of terminal 2-k.

Next, 1-th to n-th transmit weight generation sections 6-1 to 6-ngenerate pieces of transmit weight information according to differentweight generation algorithms (Step S32).

Beam selection section 7 selects the transmit weight information thatmaximizes a predetermined criterion from among the pieces of transmitweight information (Step S33). The transmit weight information generatedfor k-th terminal 2-k by n-th transmit weight generation section 6-n isreferred to as transmit weight Wn(j) where j=1 to Nu(k); Nu(k) is thenumber of spatial division multiplexing streams to be transmitted toterminal 2-k; and k=1 to s. Wn(j) is a column vector having Nt elementsand the norm is normalized to 1 (except for a zero weight). When thetotal number of spatial division multiplexing streams is Ns, the totalnumber of Nu(k) to be transmitted to all terminals 2-1 to 2-s to beconcurrently connected by spatial division multiplexing is equal to Ns.

Transmit power determination section 8 determines a transmit powerdistribution factor for each spatial stream based on the transmit weightinformation selected by beam selection section 7. The sum of thetransmit powers for all the spatial streams is required not to exceed apredetermined transmit power level. Power factor multipliers 10-1 to10-s multiply the signal output of each of transmission signalgeneration sections 3-1 to 3-s by the corresponding one of the powerdistribution factors determined by transmit power determination section8 (Step S34).

Transmit beam formation section 9 generates baseband symbol data bymultiplying each of the transmission data frame sequence signals by atransmit weight used to form the selected beam, based on the transmitweight information from beam selection section 7. After this, intransmit beam formation section 9, digital data, which are the basebandsymbol data, are digital-analog converted by the unillustrateddigital-analog converter, filtered by the unillustrated band limitingfilter, and converted into carrier frequencies by the unillustratedfrequency converter, thereby being outputted as radio frequency signals.Wireless base station antennas 11-1 to 11-s emit the received radiofrequency signals to the unillustrated propagation paths (space) (StepS35).

Such is a brief description of the operation for wireless base stationdevice 1 to perform spatial division multiplexing transmission of thedownlink shown in the flowchart of FIG. 3. The items [1] to [3] beloware described in detail as follows.

[1] Transmit weight generation algorithms implemented in transmit weightgeneration sections 6-1 to 6-n

[2] How beam selection section 7 selects transmit weight information

[3] How to determine the transmit power distribution factor

A detailed description on [1] Transmit weight generation algorithmsimplemented in transmit weight generation sections 6-1 to 6-n

The transmit weight generation algorithms implemented in transmit weightgeneration sections 6-1 to 6-n are described in detail as follows.Transmit weight generation sections 6-1 to 6-n implement the followingthree basically different weight generation algorithms.

Type A: An algorithm to generate transmit weights which can improve thereception quality of a predetermined terminal 2 with a restriction tominimize the interference to the other terminals 2

Type B: An algorithm to generate transmit weights which can improve thereception quality of a predetermined terminal 2 without a restriction toreduce the interference to the other terminals 2

Type C: An algorithm to generate a single transmit weight

It has turned out through simulations that the use of the threedifferent algorithms can generate transmit weights that can meet variouslevels of correlation conditions between the terminals. FIGS. 6 to 8 aregraphs showing simulation results of the relationship between thespatial correlation coefficient “ρ” and communication quality when anexit angle difference AOD (2) (described later) between the terminals ischanged so as to change the spatial correlation coefficient “ρ” betweenthe terminals. The simulation is performed under the conditions of FIG.5 in directional channel models shown in FIGS. 4A to 4E. The requiredtransmit power which satisfies “bit error rate (BER)=1×10^(−3n) is usedas the communication quality evaluation value (note that normalizationis performed by the transmit power for single antenna transmission). Asthe value is smaller, the communication quality of the type is better.

FIG. 4A shows an antenna element arrangement of wireless base stationantenna 60, and FIG. 4B shows an antenna element arrangement ofreceiving unit antenna 62 of a terminal when these elements are used ina simulation. In wireless base station antenna 60, four transmit antennaelements 60-1 to 60-4 are arranged at regular intervals of “Dt” on astraight line. In receiving unit antenna 62, two receiving antennaelements 62-1 to 62-2 are arranged at regular intervals of “Dr”.

FIG. 4C is a diagram showing how the radio wave radiated from wirelessbase station antenna 60 is reflected at reflection point 65 by obstacle64 and received by receiving unit antenna 62 via path 67-a and path67-b. Path 67-a indicates the direction of the radio wave to be radiatedtoward obstacle 64. Path 67-b indicates the direction of the radio waveto be radiated from reflection point 65 of obstacle 64. The angle, whichis formed between the normal of the straight line connecting transmitantenna elements 60-1 to 60-4 on the side of obstacle 64 and path 67-a,is defined as an exit angle difference AOD. The angle, which is formedbetween the normal line of the straight line connecting receivingantenna elements 62-1 and 62-2 on the side of obstacle 64 and path 67-b,is defined as an incident angle difference AOA.

The communication path between wireless base station antenna 60 andreceiving unit antenna 62 of the k-th terminal (user) is referred to asthe k-th user path. The AOD and the AOA in this case are referred to asan AOD (k) and an AOA (k), respectively. The k-th user path consists ofpath 67-a and path 67-b.

FIGS. 4D and 4E are diagrams showing a beam width on the transmittingside of path 67-a and a beam width on the receiving side of path 67-b,respectively. The horizontal axis represents the beam width and thevertical axis represents the field strength. The width between the peakvalue of the field strength and a point 3 dB below the peak value isdefined as a beam width. The angle spread on the transmitting side isdefined as AS(t) and the angle spread on the receiving side is definedas AS(r). When the wireless base station antenna height is greater thanthe surrounding building height, AS(r) tends to be larger than AS(t).

FIG. 6 shows the case where Ricean factor K=3 dB. In FIG. 6, thehorizontal axis represents the spatial correlation coefficient “ρ”between the terminals, and the vertical axis represents the requiredtransmit power as signal quality which satisfies “bit error rate(BER)=1×10^(−3n). The relationship between the signal quality and thespatial correlation coefficient between the terminals is plotted withblack squares for Type A; with black triangles for Type B; and whitecircles for Type C.

In FIG. 6, the value of the spatial correlation coefficient “ρ” at theintersection of Type B and Type A is referred to as E1, and the value ofthe spatial correlation coefficient “ρ” at the intersection of Type Band Type C is referred to as F1. The signal quality of each of Types Ato C changes as follows so as to show the spatial correlationcoefficient-to-communication quality characteristics in FIG. 6. Type Bhas the best communication quality when the spatial correlationcoefficient “ρ” is from 0 to E1; Type A has the best communicationquality when the coefficient “ρ” is from E1 to F1; and Type C has thebest communication quality when the coefficient “ρ” is from F1 to 1.

FIG. 7 shows the case where Ricean factor K=6 dB, and FIG. 8 shows thecase where Ricean factor K=9 dB. Both cases have results similar to thecase shown in FIG. 6. More specifically, regardless of the value of theRicean factor K, the spatial correlation coefficient-to-communicationquality characteristics can be divided into three or more regions, andin each of the regions, one of Types A to C has the best communicationquality.

A Ricean factor K is a parameter showing line-of-sight conditionsbetween wireless base station antenna 60 and receiving unit antenna 62.In general, when a Ricean factor K is large, the wireless base stationantenna height is large, indicating a propagation model in the cellularenvironment which is relatively likely to be in line-of-sightenvironments. When the Ricean factor K is small, on the other hand, bothwireless base station antenna 60 and receiving unit antenna 62 are lowerin height than the surrounding buildings, indicating a propagation modelnot in line-of-sight environments.

These results indicate the following. When the correlation between theterminals is low (for example, the spatial correlation coefficient “ρ”is 0 or more and 0.3 or less), it is advantageous to use Type B, whichuses the degrees of freedom of the antennas on the transmitting side toimprove the communication quality with terminals 2.

When the correlation is very high (for example, the spatial correlationcoefficient “ρ” is 0.8 or more and 1 or less), it is advantageous to useType C, which does not involve spatial division multiplexingtransmission. When the correlation is intermediate (for example, thespatial correlation coefficient “ρ” is 0.4 or more and 0.6 or less), itis advantageous to use Type A, which uses the degrees of freedom of theantennas on the transmitting side to eliminate the interference betweenthe terminals. More specifically, in order to select one of theaforementioned three algorithms according to the spatial correlationcoefficient “ρ”, the second type (Type B) is selected when the spatialcorrelation coefficient “ρ” is in the region where 0≦ρ≦0.3; the firsttype (Type A) is selected when the coefficient “ρ” is in the regionwhere 0.4≦ρ≦0.6; and the third type (Type C) is selected when thecoefficient “ρ” is in the region where 0.8≦ρ≦1. Thus, the most effectivealgorithm can be selected from among the different algorithms accordingto the spatial correlation coefficient so as to maintain highcommunication quality, thereby achieving spatial division multiplexingtransmission.

Type A algorithm includes algorithms (A-1), (A-2), and (A-3). Algorithm(A-1), which is used in the case where terminals 2 have a singleantenna, includes null beam forming (ZF (Zero-Forcing) beam) to steer anull in the direction toward other terminals 2 and a MMSE(Minimum-Mean-Square-Error) beam. Algorithms (A-2) and (A-3) are used inthe case where terminals 2 have a plurality of antennas. Algorithm (A-2)is a block diagonalization weight algorithm. Algorithm (A-3) is a jointweight generation algorithm in which block diagonalization is performedon the assumption that a reception weight is received using maximumratio combining reception weight.

Type B algorithm includes algorithms (B-1) and (B-2). The algorithm(B-1) is eigenvector beamforming which uses right singular vectorscorresponding to the same number of singular values as the number ofspatial division multiplexing streams Nu(k) to be transmitted to k-thterminal 2-k as singular values obtained by performing a singular valuedecomposition of channel estimation matrix H(k) on k-th terminal 2-k.The algorithm (B-2) is the selection of the beam whose main beamdirection is nearest to the direction of the specific terminal 2 towhich to perform spatial division multiplexing transmission. The beam isselected from among a plurality of fixed beam patterns having differentmain beam directivities from each other. The fixed beam patterns can be,for example, orthogonal beam patterns or beam patterns having differentmain beam directions at regular intervals.

Type C algorithm includes a single transmit weight algorithm in which aneigenvector beam is transmitted only to a single terminal 2 having thehighest priority of terminals 2-1 to 2-s, and a zero weight having allzero elements is generated for the other terminals 2.

The following is a detailed description of each weight generationalgorithm included in Type A algorithm.

(A-1) Null beam forming to steer a null in the direction toward otherterminals 2:

When a ZF beam is formed, transmit weight Wk(j) on k-th terminal 2-k iscalculated as follows. Transmit weight Wk(j) where j=1 to Nu(k); Nu(k)is the number of spatial division multiplexing streams to be transmittedto terminal 2-k; and s is the total number of terminals to be connectedby spatial division multiplexing satisfies Equation 1 below. Transmitweight Wk(j) is calculated for channel estimation matrices H(I) of allterminals 2 to be concurrently connected except for channel estimationmatrix H(k) on k-th terminal 2-k.

H(l)Wk(j)=0  Equation 1

However, when the number of spatial division multiplexing streams to betransmitted to terminal 2-1 is, for example, Nu(1)=3, values satisfyingEquation 1 are calculated on three elements W1(1) to W1(3) composingcolumn vector W1(j), which is the transmit weight on terminal 2-1.

As described above, k is varied from 1 to s so as to calculate all thetransmit weights on terminals 2-1 to 2-s. In other words, Ns transmitweights, the same number as the total number of spatial divisionmultiplexing streams, are calculated.

When a MMSE beam is formed, all terminals 2 on the receiving side areassumed to have an equal noise power δ² and set to a predeterminedvalue, thereby generating transmit weight Wn(j) which satisfies Equation2 and Equation 3 maximizing the signal-to-interference power ratio (SIR)in each of terminals 2 where j=1 to s, and s is the total number ofterminals to be connected by spatial division multiplexing.

$\begin{matrix}{F = {{\left( {{Q^{H}Q} + {\frac{\sigma^{2}}{N_{t}}I}} \right)^{- 1}Q^{H}} = \left\lbrack {{W_{n}(1)}{W_{n}(2)}\mspace{14mu} \ldots \mspace{14mu} {W_{n}(S)}} \right\rbrack}} & {{Equation}\mspace{14mu} 2} \\{Q = \begin{bmatrix}{H(1)} \\{H(2)} \\\vdots \\{H(s)}\end{bmatrix}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

where the superscript “H” indicates a complex conjugate.

(A-2) Block diagonalized weight algorithm:

Transmit weight Wn(j) where j=1 to Nu(k) on k-th terminal 2-k iscalculated as follows. First, matrix Dk shown in Equation 4 is generatedas a new matrix based on channel estimation matrices H(I) where I=1, 2,. . . s, and I≠k of all the terminals to be concurrently connectedexcept for channel estimation matrix H(k) on k-th terminal 2-k.

$\begin{matrix}{D_{k} = \begin{bmatrix}{H(1)} \\\vdots \\{H\left( {k - 1} \right)} \\{H\left( {k + 1} \right)} \\\vdots \\{H(s)}\end{bmatrix}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Next, right singular matrix Vk shown in Equation 5 is calculated byperforming a singular value decomposition of Dk.

D _(k) =U _(k) B _(k) V _(k) ^(H)  Equation 5

Right singular matrix Vk thus obtained consists of Nt rows and Ntcolumns, and the matrix obtained by extracting the right singularvectors corresponding to the singular value “0” (a numerical zero) isreferred to as Rk. Matrix Rk consists of Nt rows and Nq columns. Nq isshown in Equation 6 below.

$\begin{matrix}{N_{q} = {N_{t} - {\sum\limits_{\underset{j \neq k}{j = 1}}^{s}{N_{r\;}(j)}}}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

Eigenvector beam transmission is performed using matrix Rk consisting ofNt rows and Nq columns based on a new matrix Ek shown in Equation 7.

E _(k) =H(k)R _(k)  Equation 7

Matrix Ek consists of Nr(k) rows and Nq columns. Nu(k) singular values,which are the same number as the total number of spatial divisionmultiplexing streams to be transmitted to k-th terminal 2-k, areselected in descending order from among the right singular vectorsobtained by performing a singular value decomposition of Ek. The rightsingular vectors corresponding to the selected singular values are usedas transmit weight Wn(j).

As described above, k is varied from 1 to s so as to calculate thetransmit weights on terminals 2-1 to 2-s. In other words, Ns transmitweights, which are the same number as the total number of spatialdivision multiplexing streams, are calculated.

(A-3) Joint weight generation algorithm in which block diagonalizationis performed on the assumption that a reception weight is received usingmaximum ratio combining reception weight:

Transmit weight Wn(j) where j=1 to Nu(k) on k-th terminal 2-k iscalculated as follows. First, as shown in Equation 8, Nu(k) singularvalues, which are the same number as the total number of spatialdivision multiplexing streams to be transmitted to k-th terminal 2-k,are selected in descending order from among left singular matrices Ukobtained by performing a singular value decomposition of channelestimation matrix H(k) on k-th terminal 2-k. The left singular vectorscorresponding to the selected singular values are used as receptionweight matrix Gk in k-th terminal 2-k. Reception weight matrix Gkconsists of Nr(k) rows and Nu(k) columns.

H(k)=U _(k) B _(k) V _(k) ^(H)  Equation 8

The calculation of reception weight matrix Gk is performed for allterminals 2.

Next, a new channel estimation matrix Dk shown in Equation 9 iscalculated using channel estimation matrices H(m) and reception weightmatrices Gm, where m=1 to s and m≠k except for channel estimation matrixH(k) and reception weight matrix G(k) on k-th terminal 2-k.

$\begin{matrix}{D_{k} = {\begin{bmatrix}{E_{1}{H(1)}} \\\vdots \\{E_{k - 1}{H\left( {k - 1} \right)}} \\{E_{k + 1}{H\left( {k + 1} \right)}} \\\vdots \\{E_{s}{h(s)}}\end{bmatrix} = \begin{bmatrix}{G_{1}^{H}{H(1)}} \\\vdots \\{G_{k - 1}^{H}{H\left( {k - 1} \right)}} \\{G_{k + 1}^{H}{H\left( {k + 1} \right)}} \\\vdots \\{G_{s}^{H}{H(s)}}\end{bmatrix}}} & {{Equation}\mspace{14mu} 9}\end{matrix}$

Next, right singular matrix Vk shown in Equation 5 is calculated onmatrix Dk thus obtained. Right singular matrix Vk thus obtained consistsof Nt rows and Nt columns, and the matrix obtained by extracting theright singular vectors corresponding to the singular value “0” (anumerical zero) is referred to as Rk. Matrix Rk consists of Nt rows andNv columns. Nv is shown in Equation 10.

$\begin{matrix}{N_{v} = {N_{t} - {\sum\limits_{\underset{j \neq k}{j = 1}}^{s}{N_{u}(j)}}}} & {{Equation}\mspace{14mu} 10}\end{matrix}$

Eigenvector beam transmission is performed using matrix Rk consisting ofNt rows and Nv columns based on a new matrix Ek shown in Equation 7.Matrix Ek consists of Nr(k) rows and Nv columns. Nu(k) singular values,which are the same number as the total number of spatial divisionmultiplexing streams to be transmitted to k-th terminal 2-k, areselected in descending order from among the right singular vectorsobtained by performing a singular value decomposition of Ek. The rightsingular vectors corresponding to the selected singular values are usedas transmit weight Wn(j). As described above, k is varied from 1 to s soas to calculate the transmit weights on terminals 2-1 to 2-s. In otherwords, Ns transmit weights, the same number as the total number ofspatial division multiplexing streams, are calculated.

Algorithm (A-3) is on the assumption that a reception weight is receivedusing maximum ratio combining reception weight so as to reduce theconstraint on the formation of a directional null. As a result, unlikethe algorithm (A-2), algorithm (A-3) can be used even when the totalnumber of the receiving antennas of terminals 2 to be concurrentlyconnected is larger than the number Nt of transmit antennas of wirelessbase station device 1. Furthermore, unlike algorithm (A-2) in which theformation of transmit weights is restricted by the number of thereceiving antennas, in algorithm (A-3) the formation of transmit weightsis restricted by the number of spatial division multiplexing streams.This provides algorithm (A-3) with an advantage of having betterreception quality than algorithm (A-2) when the number Nu(k) of spatialdivision multiplexing streams to be transmitted to terminal 2-k issmaller than the number Nr(k) of the receiving antennas of terminal 2-k.

A detailed description on [2] How beam selection section 7 selectstransmit weight information

How beam selection section 7 selects transmit weight information isdescribed in detail as follows. Beam selection section 7 selectstransmit weight information that maximizes a predetermined criterionfrom among the pieces of transmit weight information generated by firstto n-th transmit weight generation sections 6-1 to 6-n. Thepredetermined criterion can be a predicted value of physical quantityindicating the quality of signals received by terminals 2, such assignal-to-noise power ratio (hereinafter, SNR) or signal-to-interferenceand noise power ratio (hereinafter, SINR).

How to select a specific transmit weight is described as follows usingEquations. First, Ns spatial streams at time “t” is expressed byEquation 11, and signal Yn(t) to be transmitted is expressed by Equation12 on the assumption that the transmit weight information generated byn-th transmit weight generation section 6-n has been selected where k=1to Ns, and Yn(t) is a column vector consisting of Nt elements. Equation13 shows the transmit power for each of the spatial divisionmultiplexing streams to be transmitted to terminals 2-1 to 2-s, and thetransmit power is assumed to be uniform. Wn(k) is a transmit weight (acolumn vector having Nt elements) on k-th spatial stream (Equation 11)generated by n-th transmit weight generation section 6-n.

s _(k)(t)  Equation 11

where the subscript “k” indicates the k-th spatial stream and k=1, 2, .. . , Ns.

$\begin{matrix}{{Y_{n}(t)} = {\begin{bmatrix}{W_{n}(1)} & {W_{n}(2)} & \ldots & {W_{n}({Ns})}\end{bmatrix}{\quad{\begin{bmatrix}P_{1} & 0 & \ldots & 0 \\0 & P_{2} & \ddots & \vdots \\\vdots & \ddots & \ddots & 0 \\0 & \ldots & 0 & P_{Ns}\end{bmatrix}\begin{bmatrix}{s_{1}(t)} \\{s_{2}(t)} \\\vdots \\{S_{Ns}(t)}\end{bmatrix}}}}} & {{Equation}\mspace{14mu} 12} \\{\mspace{79mu} P_{k}} & {{Equation}\mspace{14mu} 13}\end{matrix}$

where the subscript “k” indicates the k-th spatial stream and k=1, 2, .. . , Ns.

Next, a reception signal (Equation 14) of terminals 2 is predicted. Thereception signal (Equation 14) can be expressed by Equation 15 usingchannel information H(k) on k-th terminal 2-k.

Z _(k)(t)  Equation 14

Z _(k)(t)=H(k)Y _(n)(t)  Equation 15

When the number Nr(k) of antennas of terminal 2-k is 1, the SINR isobtained by Equation 16. The symbol “δ” represents a noise power on theassumption that Gaussian additive noise is added to the interference,and is hereinafter treated as a predetermined fixed value.

$\begin{matrix}{{{SINR}_{n}(k)} = \frac{{{{H(k)}{W_{n}(k)}}}^{2}}{{\sum\limits_{{j = 1},{j \neq k}}^{Ns}{{{H(k)}{W_{n}(j)}}}^{2}} + \sigma^{2}}} & {{Equation}\mspace{14mu} 16}\end{matrix}$

When terminal 2-k has more than one antenna, SINR estimation isperformed using Equation 17 on the assumption that the directivity isformed using reception weight R(k). Reception weight R(k) represents acolumn vector having Nr(k) elements the same number as the number ofreceiving unit antennas of terminal 2-k. In Equation 17, the subscript“n” represents the number of user terminals, that is, the total numberof terminals 2 to be connected by spatial division multiplexing, whichcorresponds to terminals 2-1 to 2-s in the present embodiment.

$\begin{matrix}{{{SINR}_{n}(k)} = \frac{{{{R(k)}{H(k)}{W_{n}(k)}}}^{2}}{{\sum\limits_{{j = 1},{j \neq k}}^{Ns}{{{R(k)}{H(k)}{W_{n}(j)}}}^{2}} + {\sigma^{2}{{R(k)}}^{2}}}} & {{Equation}\mspace{14mu} 17}\end{matrix}$

In order to calculate a virtual reception weight in terminals 2, it ispossible to use MMSE algorithm or ZF algorithm when there is aninterference component, and to use a maximum ratio combining receptionweight when there is no need to consider an interference component.

When the block diagonalization weight algorithm is used to calculate atransmit weight, the same number of singular values as the number ofspatial division multiplexing streams to be transmitted to terminal 2-kare selected in descending order from among the singular values obtainedby performing a singular value decomposition of channel estimationmatrix H(k). The left singular vectors corresponding to the selectedsingular values can be used.

Another possible algorithm is to prepare a plurality of weightinformation candidates to be used as the aforementioned reception weightand to apply SINR estimation to each candidate, thereby selecting theoptimum combination of a reception weight and a transmit weightcandidate. This algorithm requires a large processing capacity for theSINR estimation, but it is possible to obtain the best communicationquality in various propagation environments.

Through the aforementioned calculations, SINRn(k) of each user iscalculated using Wn(k) expressed by Equation 17 as a variable. SINRn(k)is calculated for all of the first to n-th transmit weight generationsections. Then, beam selection section 7 selects transmit weight Ws(k)where k=1 to Ns. Transmit weight Ws(k) is the output information of s-thtransmit weight generation section 6-s which generates the transmitweight making the total SINRn(k) of all users largest.

It is possible to perform weighting-adding according to the QoS(allowable delay, transmission request rate, or the like) of spatialdivision multiplexing streams. For example, a high weighing is given toa user (terminal) which requires real-time signal transmission with asmall allowable delay so as to provide preferential signal transmission.This reduces the number of retransmission times, thereby improving totalsystem throughput.

It is alternatively possible to perform weighting-adding according tothe transmission request rate. For example, a high weighting coefficientis given to a spatial division multiplexing stream having a hightransmission request rate so as to provide preferential signaltransmission. This improves total system throughput.

A detailed description on [3] How to determine the transmit powerdistribution factor

How to determine the transmit power distribution factor is described indetail as follows. Although the power distribution can be simply basedon equal power distribution, it is possible to utilize the followingalgorithms (1) and (2) to improve throughput or to reduce transmitpower.

(1) An algorithm to improve capacity (throughput):

SNR(k) is measured as the reception quality of terminal 2-k to receive abroadcast signal from wireless base station device 1, and the measuredinformation is notified in advance to wireless base station device 1.Water-filling algorithm is used based on a theoretical capacity obtainedthrough the calculation of each SNR(k) and each channel estimationmatrix. The water-filling algorithm is an algorithm for distributingpower preferentially to streams with a good SNR value. As a result, apower distribution ratio is determined for each spatial stream and isused as a power distribution factor.

In this technique, the power distribution ratio is preferably correctedbecause in general the power distribution ratio takes discrete valuesaccording to changes in modulation level and coding rate (hereinafter,MCS). In that case, the following correction algorithm is used. A SINRto be received by terminal 2-k is predicted. When the predicted SINRexceeds a required SINR in the MCS that achieves the maximum rate, thesurplus is distributed to the spatial streams to be transmitted to theother terminals 2 so as not to supply the surplus to terminal 2-k. Incontrast, when the predicted SINR is below the required SINR in the MCSthat achieves the minimum rate, the power distribution ratio for thespatial streams to be transmitted to the other terminals 2 is reduced soas to distribute power preferentially to the spatial stream to betransmitted to terminal 2-k.

(2) An algorithm to reduce transmit power:

SNR(k) is measured as the reception quality of terminal 2-k to receive abroadcast signal from wireless base station device 1, and the measuredinformation is notified in advance to wireless base station device 1.

SNR(k) thus obtained is used to estimate a noise power so as to predictSNRt(j) where j=1 to Nu(k). SNRt(j) is expressed by Equation 18 as theSNR in spatial division multiplexing stream transmission. In Equation18, Pa represents the ratio of the transmit power of a broadcast signalto a predetermined maximum power in the spatial division multiplexingstream transmission; and h(k) represents a column vector consisting ofthe n-th column of H(k). The column vector consists of the same numberof elements as the number Nr(k) of antennas contained in the receptionunit of terminal 2-k when the broadcast signal is transmitted from then-th antenna.

$\begin{matrix}{{{SINR}_{t}(k)} = \frac{{{{H(k)}{W_{n}(k)}}}^{2}}{P_{a}{h^{H}(k)}{h(k)}}} & {{Equation}\mspace{14mu} 18}\end{matrix}$

The following process is performed in wireless base station device 1 onthe assumption that wireless base station device 1 has a table showingthe relationship between reception quality (SNR) and the optimum MCS interminals 2. First, power distribution to terminals 2 is performed indescending order of data transmission priority from all terminals 2 tobe concurrently connected according to each allowable delay required asa part of QoS. Then, a required SNR to satisfy the minimum transmissionrate is determined, after a predetermined margin is added, from the MCScombinations that achieve the transmission rate satisfying the allowabledelay.

Then, power distribution factor b(j) is determined in such a manner thatSNRt(j), which is the SNR in the spatial division multiplexing streamtransmission, can be nearly equal to the required SNR. When b(j) issmaller than 1, power is uniformly distributed within the surplustransmit power to the other spatial streams or to the other terminals 2to be concurrently connected, and no transmission is made to terminals 2that do not satisfy the required SNR. Eventually, the power distributionis performed so that the total of power distribution factors b(k) is 1or less.

The operation of transmission signal generation sections 3-1 to 3-s isdescribed in detail as follows. First, first to s-th transmission signalgeneration sections 3-1 to 3-s generate signals (hereinafter,transmission data sequences) to be transmitted to terminals 2-1 to 2-sconnected by spatial division multiplexing (preferably allocated). Eachtransmission data sequence is error-correction encoded by anunillustrated error correction encoder, interleaved by an unillustratedinterleaver, punctured by an unillustrated puncturer, and symbol mappedby an unillustrated modulator in accordance with a predeterminedmodulation system. Hereinafter, the symbol mapped signal is referred toas a symbol data sequence or a spatial stream individual data signal.After this, each symbol data sequence is provided with a known pilotsignal and control information so as to generate a transmission signalhaving a predetermined frame structure. Hereinafter, the transmissionsignal is referred to as a transmission data frame sequence.

FIG. 9B shows a structure of a transmission data frame sequence.Transmission data frame sequences 500-1 to 500-s generated and outputtedrespectively by first to s-th transmission signal generation sections3-1 to 3-s consist of control information sections C1 to Cs,respectively, and spatial stream sections K1 to Ks, respectively.Spatial stream sections K1 to Ks consist of spatial stream individualpilot signal sections P1 to Ps, respectively, and spatial streamindividual data signal sections D1 to Ds, respectively.

Control information sections C1 to Cs, which are signals to be broadcastto all terminals 2-1 to 2-s to be connected by spatial divisionmultiplexing, are transmitted omnidirectionally. Control informationsections C1 to Cs contain the number of spatial streams followingthereto; the ID information of the designation terminals correspondingto spatial stream numbers, that is, the information to associate eachspatial stream with the transmission data sequence to be transmitted toeach terminal; and modulation format information such as coding method,coding rate, modulation level, and data length.

On the other hand, spatial stream sections K1 to Ks, which are signalsto be transmitted to terminals 2-1 to 2-s, respectively, using atransmit weight, are transmitted directionally. Spatial stream sectionsK1 to Ks have a preamble structure in which spatial stream individualpilot signal sections P1 to Ps each consisting of a known pilot signalsequence are added to the previous stage of the spatial streamindividual data signal sections D1 to Ds containing the transmissiondata (individual data) to be transmitted to each terminal. The preamblestructure may be replaced by a postamble structure in which sections P1to Ps are added to the subsequent stage of sections D1 to Ds, or amidamble structure in which sections P1 to Ps are added in the middle ofsections D1 to Ds.

FIG. 9A is a schematic diagram showing the spatial division multiplexingtransmission of the aforementioned transmission data frame sequences toterminals 2-1 to 2-s (corresponding to the first to s-th users) alongthe temporal and spatial axes. The diagram indicates that controlinformation 40-1 to 40-s is transmitted omnidirectionally to all theusers (the first to s-th users) to be connected by spatial divisionmultiplexing, and then an individual signal is transmitted directionallyto each of the users (the first to s-th users). The time from T1 to T2corresponds to the time required to transmit a single transmission dataframe sequence.

FIG. 10B shows a structure of a second transmission data frame sequence.Unlike the frame structure of FIG. 9B, the spatial stream sectionsinclude spatial stream individual control information sections SC1 toSCs. Spatial stream individual control information sections SC1 to SCsinclude the modulation format information of the subsequent spatialstream individual data signal sections D1 to Ds. The modulation formatinformation is transmitted by a fixed predetermined modulation format.

Using this structure makes it unnecessary for control informationsections C1 to Cs to contain the modulation format information of thesubsequent spatial stream individual data signal sections D1 to Ds,thereby reducing the amount of data in control information sections C1to Cs. Furthermore, spatial stream individual control informationsections SC1 to SCs containing the modulation format information ofspatial stream individual data signal sections D1 to Ds are alsotransmitted directionally. This prevents terminals 2-1 to 2-s fromerroneously receiving the modulation format information of spatialstream individual data signal sections D1 to Ds. This ensures improvedreception quality.

Such is the detailed description of items [1] to [3].

The operation of terminals 2-1 to 2-s to receive spatially-multiplexedtransmitted signals from wireless base station device 1 is described asfollows with reference to FIGS. 2A and 2B. The following is adescription of the operation after (frame and symbol) synchronization isestablished with wireless base station device 1.

First, in terminal 2-A, radio frequency signals received by receivingunit antennas 20-1 to 20-m are inputted to reception sections 221-1 to221-m. Reception sections 221-1 to 221-m filter a predetermined bandfrom the radio frequency signals; frequency-convert the radio frequencysignals into quadrature-detected baseband signals; and output digitalsignal data (hereinafter, complex baseband signals) consisting of Isignals and Q signals through a digital-analog converter (hereinafter,A/D converter).

Spatial division demultiplexing section 223 receives the data signalhaving a predetermined spatial stream number notified to its ownterminal from the received one or more complex baseband signals. Then,spatial division demultiplexing section 223 either eliminates the otherdata signals having the spatial stream numbers other than it ownterminal, that is, interference signals, or reduces it to a level thatcan ensure signal quality sufficient for transmission. To achieve this,spatial division demultiplexing section 223 operates as follows.

First, in channel estimation section 222, all of the spatial streamindividual pilot signals are separated and extracted from the spatialstreams at the arrival timing of pilot signals that are transmittedattached to the respective spatial streams (hereinafter, spatial streamindividual pilot signals), thereby calculating the channel estimationvalues of the propagation paths. M-th terminal 2-m, which receives aspatially multiplexed signal, includes Nr(m) receiving unit antennas20-1 to 20-m and Nr(m) reception sections 221-1 to 221-m correspondingthereto, respectively.

When the k-th spatial stream individual pilot signal sequence (Equation19) is received by j-th receiving unit antenna 20-j and receptionsection 221-j of m-th terminal 2-m, the output signal (Equation 20) isobtained. When a correlation calculation is performed between the outputsignal and Equation 19 generated in terminal 2-m as shown in Equation21, a channel estimation value (Equation 22) of a propagation path canbe determined.

AP _(k)(t)  Equation 19

r _(j,k) ^((m))(t)  Equation 20

where j=1, . . . , Nr(m); k=1, . . . , Ns; and Nr(m) is the number ofreceiving unit antennas.

$\begin{matrix}{{h^{m}\left( {j,k} \right)} = {\sum\limits_{t = 1}^{N_{p}}{{{AP}_{k}^{*}(t)}{r_{j,k}^{(m)}(t)}}}} & {{Equation}\mspace{14mu} 21}\end{matrix}$

where Np is the number of symbols of spatial stream individual pilotsignal sequences, and the superscript asterisk “*” indicates an operatorto perform complex conjugate multiplication.

h^(m)(j,k)  Equation 22

It is possible to store the results of a plurality of times of receptionof spatial stream individual pilot signal sequences (Equation 19) and toperform averaging. In that case, if the travel speed of terminal 2-m islow enough, this can reduce noise influence and increase the channelestimation quality of the propagation path.

Finally, channel estimation values (Equation 22) of a total of Ns×Nr(m)propagation paths are calculated as the channel estimation values of thepropagation paths of m-th terminal 2-m where Ns represents the number ofspatial division multiplexing streams and Nr(m) represents the number ofreceiving unit antennas of terminal 2-m.

The channel estimation matrix (Equation 23) on terminal 2-m is definedby Equation 24.

$\begin{matrix}H^{m} & {{Equation}\mspace{14mu} 23} \\{H^{m} = \begin{bmatrix}{h^{m}\left( {1,1} \right)} & {h^{m}\left( {1,2} \right)} & \ldots & {h^{m}\left( {1,N_{t}} \right)} \\{h^{m}\left( {2,1} \right)} & {h^{m}\; \left( {2,2} \right)} & \ldots & {h^{m}\left( {2,N_{t}} \right)} \\\vdots & \vdots & \vdots & \vdots \\{h^{m}\left( {N_{s}^{(m)},1} \right)} & {h^{m}\left( {N_{s}^{(m)},2} \right)} & \ldots & {h^{m}\left( {N_{s}^{(m)},N_{t}} \right)}\end{bmatrix}} & {{Equation}\mspace{14mu} 24}\end{matrix}$

Then, spatial multiplexed channels are separated using the obtainedchannel estimation matrix (Equation 23). The separation of spatialmultiplexed channels involves the same operations as the separation andextraction of the data signal from each spatial division multiplexingstream.

The algorithm used for the separation can be, for example, ZF (ZeroForcing) using the inverse matrix of the channel estimation matrix, orMMSE (Minimum Mean Square Error).

When ZF algorithm is applied to a reception signal (Equation 25) of j-threceiving unit antenna 20-j and reception section 221-j in m-th terminal2-m, row vector V(Bm) consisting of the (Bm)-th row in (H^(m))⁻¹, whichis the inverse matrix of H^(m), is calculated. Row vector V(Bm) isregarded as the reception weight used to receive a predetermined spatialdivision multiplexing stream.

r _(j) ^((m))(t)  Equation 25

where j=1, . . . , Nr(m); and Nr(m) is the number of receiving unitantennas.

Bm represents a spatial stream number to be transmitted to terminal 2-mnotified from wireless base station device 1. The data signal having theBm-th spatial stream number can be extracted as a desired signal asfollows: Reception weight V(Bm) is multiplied by a spatial streamreceiving signal in terminal 2-m (Equation 27) as shown in Equation 26so as to suppress the interference signals from the other spatialstreams.

z _(B) _(m) ^(m)(t)=V(B _(m))r ^(m)(t)  Equation 26

r ^((m))(t)  Equation 27

where r^((m))(t) is a column vector having rj^((m)) (t) where j=1, . . ., Nr(m) as the j-th element. The j-th element rj^((m)) (t) is receivedby the j-th antenna and reception section 221-j in m-th terminal 2-m.

Next, the case of using MMSE algorithm is described. In the same manneras in ZF algorithm, row vector V(Bm) consisting of the Bm-th row ofreception weight matrix W calculated according to the MMSE standard isdetermined. Then, row vector V(Bm) is regarded as the reception weightused to receive a predetermined spatial stream.

The Bm-th spatial stream can be received as a desired signal bymultiplying the reception weight by the spatial stream receiving signal(Equation 27) in terminal 2-m as shown in Equation 26 so as to suppressthe interference signal components from the other spatial streams.

When there are a plurality of spatial stream numbers to be transmittedto the same terminal 2-m, reception weights used to receive the datasignals having these spatial stream numbers are generated and multipliedby the spatial stream receiving signal (Equation 27). As a result, adesired signal can be received after being separated from each spatialstream.

When information about the modulation and coding such as the coding rateand the modulation level of the spatial stream data to be transmitted tothe terminals other than terminal 2-m is known, it is possible to usemaximum likelihood estimation (connection estimation), successive (orserial)-interference-canceller (for example, V-BLAST) or otheralgorithms.

Demodulation section 224 performs demodulation and decoding of a desiredsignal received after being separated from the spatial divisionmultiplexing stream, thereby restoring a predetermined transmission datasequence.

Terminal 2-B having only one receiving unit antenna 20-1 as shown inFIG. 2B cannot eliminate spatial interference due to the absence ofspatial division demultiplexing section 223. Therefore, demodulationsection 224 performs demodulation while compensating the influence dueto environmental changes of the propagation path. The demodulation isperformed using the channel estimation value obtained by channelestimation section 222 from the signal received by reception section221-1.

As described above, in the present first embodiment, it is possible toselect a transmit weight that can improve the spatial divisionmultiplexing transmission with terminals 2-1 to 2-s in accordance withvarious spatial correlation conditions and also improve the receptionquality of terminals 2-1 to 2-s each having a plurality of antennas. Asa result, system capacity can be increased by spatial divisionmultiplexing transmission.

Furthermore, in the process to allocate terminals 2 to be preferentiallyconnected by spatial division multiplexing, it is unnecessary to performthe control of combination allocation of terminals 2 based on thedetection of the spatial correlation coefficient, which isconventionally performed by the wireless base station device, and it isonly necessary to perform preferential user allocation process by apacket scheduler. This simplifies the scheduling process for terminals 2to be connected by spatial division multiplexing.

When terminal 2 has a plurality of receiving unit antennas as interminal 2-A, wireless base station device 1 transmits known pilotsignals by being associated with the corresponding spatial streams, andreception unit 220 of terminal 2 performs channel estimation using thepilot signals. Consequently, when transmit weights are generated bywireless base station device 1, even if there is a channel estimationerror or an environmental change in the propagation path, that is, atemporal change in the channel, deterioration of communication qualitydue to the changes can be reduced.

In the case of the TDD system, using the feature of “reciprocity in apropagation path” allows the use of the channel estimation result of theuplink as the channel estimation value of the downlink. In that case, itis necessary to fully correct the deviation between thetransmission-reception system of the uplink and thetransmission-reception system of the downlink including an antenna fortransmission and reception and a radio frequency (RF) circuit. However,the correction is generally insufficient, so that in many cases there isan error between the systems. Therefore, the present algorithm, MMSE,can be applied to reduce the deterioration of communication quality dueto the influence of the error between the systems.

In the present first embodiment, after transmit weight generationsections 6-1 to 6-n generate respective transmit weights, beam selectionsection 7 selects a transmit weight based on the predicted SINR.Alternatively, however, it is possible to calculate the spatialcorrelation coefficient between the terminals, and then to determine thetransmit weight based on an average value or a minimum value.

In this case, a transmit weight generation algorithm that is optimum forthe spatial correlation conditions between the terminals is selectedquicker than the convention method based on the following fact. There isa specific relationship between three basically different algorithms fortransmit weight generation about the spatial correlationcoefficient-to-communication quality characteristics. Thecharacteristics are divided into a plurality of regions according to thespecific relationship, and an algorithm providing the best communicationquality is selected in each of the regions automatically from among thethree algorithms.

More specifically, the transmit weight can be easily selected throughthe following two steps: A step of extracting channel informationbetween the terminals and the wireless base station device from thereception signals received from the terminals, thereby determining aspatial correlation coefficient between the terminals with which thewireless base station device performs spatial division multiplexingtransmission based on the channel information. The other step ofpreviously determining a method for selecting an algorithm providing thebest communication quality in each region from among the three transmitweight generation algorithms, and selecting the algorithm providing thebest communication quality based on this selection method and on thespatial correlation coefficient determined by the former step.

In the present first embodiment, both single-carrier transmission andmulticarrier transmission can be achieved. Multicarrier transmission canbe achieved by calculating a channel estimation value for everysubcarrier and performing the separate reception of spatial divisionmultiplexing streams for every subcarrier as done in the presentembodiment. Multicarrier transmission can be applied regardless of theduplex mode such as TDD or FDD, and the access mode such as TDMA, FDMA,or CDMA.

As described hereinbefore, according to the present first embodiment,there is provided transmit weight determination section 5. Transmitweight determination section 5 can change the algorithm to generatetransmit weights which are used for wireless base station device 1 toperform spatial division multiplexing transmission with terminals 2-1 to2-s based on the channel information. The presence of transmit weightdetermination section 5 can improve and ensure the communication qualityunder various spatial correlation conditions and hence can increasesystem capacity by spatial division multiplexing transmission.

The presence of transmit weight determination section 5 can also changethe transmit weight generation algorithm depending on the spatialcorrelation conditions between the terminals so as to achieve spatialdivision multiplexing transmission robust to the spatial correlationconditions between the terminals. This simplifies the conventionalallocation process based on the spatial correlation coefficient. As aresult, wireless base station device 1 can be simplified and theprocessing time required to control the spatial division multiplexingtransmission can be reduced.

Wireless base station device 1 may have the function of performingspatial division multiplexing transmission using the followingcomponents: transmit weight generation sections 6-1 to 6-n; beamselection section 7; and transmit beam formation section 9. Transmitweight generation sections 6-1 to 6-n generate pieces of transmit weightinformation according to different algorithms. The sets of transmitweight information are used to form transmit beams to be transmitted toterminals 2-1 to 2-s with which wireless base station device 1 performsspatial division multiplexing transmission based on the channelinformation on terminals 2-1 to 2-s. Beam selection section 7 selectsone of pieces of transmit weight information generated according to thedifferent algorithms. Transmit beam formation section 9 forms thetransmit beams using the selected transmit weight information as thetransmit weight. As a result, it becomes possible to improve and ensurethe communication quality under various spatial correlation conditionsand hence to increase system capacity by the spatial divisionmultiplexing transmission.

It is also possible to select a transmit weight generation algorithmthat is optimum to the spatial correlation conditions between theterminals. This achieves spatial division multiplexing transmissionrobust to the spatial correlation conditions between the terminals,thereby simplifying the conventional allocation process based on thespatial correlation coefficient. As a result, wireless base stationdevice 1 can be simplified and the processing time required to controlthe spatial division multiplexing transmission can be reduced.

Transmit power determination section 8 may have the function ofdetermining transmit powers for the spatial division multiplexingsignals to be transmitted to terminals 2-1 to 2-s based on the selectedtransmit weight information. This allows to select an optimum one of thedifferent transmit weight generation algorithms and to generate atransmit weight that is optimum for the spatial correlation conditionsdetected from the channel information according to the selected transmitweight generation algorithm at the time of spatial division multiplexingtransmission to terminals 2-1 to 2-s. The structure also allows tocontrol the powers required to transmit the signals using these transmitweights. This makes it possible to perform transmission using signalpower to satisfy predetermined communication quality, that is, withoutusing more than necessary transmit power, thereby reducing co-channelinterference and increasing system capacity.

Beam selection section 7 may have the function of selecting transmitweight information to be used as a transmit weight, based on theinformation indicating the signal-to-interference-noise and power ratioof terminals 2. As a result, it becomes possible to improve and ensurethe communication quality under various spatial correlation conditionsand hence to increase system capacity by the spatial divisionmultiplexing transmission.

Beam selection section 7 can also have the function of selecting atransmit weight by using a predicted reception weight of terminal 2 whenterminal 2 has a plurality of receiving unit antennas 20-1 to 20-m. Thepredicted reception weight represents a prediction of a reception weightof terminal 2. As a result, it becomes possible to improve and ensurethe communication quality under various spatial correlation conditionsand hence to increase system capacity by the spatial divisionmultiplexing transmission.

The predicted reception weight may be a weight used to form a maximumratio combining reception beam. This allows to improve and ensure thecommunication quality under various spatial correlation conditions andhence to increase system capacity by the spatial division multiplexingtransmission.

The predicted reception weight can be a left singular vector obtained byperforming a singular value decomposition of a channel estimationmatrix. As a result, the transmit weight that maximizes the receivedpower can be determined while suppressing the co-channel interference.This allows to improve and ensure the communication quality undervarious spatial correlation conditions and hence to increase systemcapacity by the spatial division multiplexing transmission.

The predicted reception weight may be a weight used to form aminimum-mean-square-error beam. This allows to select a transmit weightfrom among those generated according to the different transmit weightgeneration algorithms. The transmit weight is optimum for the spatialcorrelation conditions detected from the channel information at the timeof spatial division multiplexing transmission to terminals 2-1 to 2-s.The selection of the optimum transmit weight can be performed bypredicting the reception quality when terminals 2 each having receivingunit antennas 20-1 to 20-m use left singular vectors obtained byperforming a singular value decomposition of a channel estimationmatrix.

As a result, the transmit weight information having the receptionquality that maximizes the signal-to-noise power ratio can be selectedfrom among the pieces of transmit weight information by utilizing thefollowing fact. The reception quality that maximizes the signal-to-noisepower ratio (SNR) can be obtained by using a left singular vectorcorresponding to the largest singular value among the left singularvectors obtained by performing a singular value decomposition of achannel estimation matrix.

This is effective especially in the case where the spatial correlationbetween the terminals to be concurrently connected is low so that thereis little co-channel interference. The reception weight used interminals 2 can be uniquely determined from a channel estimation matrix.When the number of spatial division multiplexing streams to betransmitted to terminal 2 is smaller than the number of receiving unitantennas of terminal 2, it is possible to select a transmit weighthaving a high transmit diversity which can reduce restrictions to reduceco-channel interference for the formation of the transmit weight. As aresult, it is possible to improve and ensure the communication qualityand hence to increase system capacity by the spatial divisionmultiplexing transmission.

The predicted reception weight may be a weight used to form a zeroforcing beam. This allows to select a transmit weight from among thosegenerated according to the different transmit weight generationalgorithms. The transmit weight is optimum for the spatial correlationconditions detected from the channel information at the time of spatialdivision multiplexing transmission to terminals 2-1 to 2-s. Theselection of the optimum transmit weight can be performed by predictingthe reception quality when terminals 2 each having receiving unitantennas 20-1 to 20-m use a minimum-mean-square-error (MMSE) beam.

As a result, the reception quality that maximizes thesignal-to-interference and noise power ratio (SINR) can be obtained byallowing terminals 2 to use a weight used to form aminimum-mean-square-error (MMSE) beam. This feature can be used toselect the transmit weight information having the reception quality thatmaximizes the signal-to-interference and noise power ratio from amongthe pieces of transmit weight information. As a result, it becomespossible to improve and ensure the communication quality under variousspatial correlation conditions in the environment where co-channelinterference exists and hence to increase system capacity by the spatialdivision multiplexing transmission.

Transmit power determination section 8 may have the function ofdetermining the transmit powers for the spatial division multiplexingsignals to be transmitted to terminals 2-1 to 2-s based on the selectedtransmit weight information. This allows to select a transmit weightfrom among those generated according to the different transmit weightgeneration algorithms. The transmit weight is optimum for the spatialcorrelation conditions detected from the channel information at the timeof spatial division multiplexing transmission to terminals 2-1 to 2-s.The selection of the optimum transmit weight can be performed bypredicting the reception quality when terminals 2 each having receivingunit antennas 20-1 to 20-m use a zero forcing(ZF) beam.

Furthermore, allowing terminals 2 to use the weight used to form a zeroforcing(ZF) beam can obtain the reception quality to form the receptionweight under a restriction to give preference to reduce the interferenceand noise power of the co-channel. This feature can be used to selectthe transmit weight information having the reception quality thatmaximizes the_signal-to-interference and noise power ratio from amongthe pieces of transmit weight information. As a result, the transmitweight that maximizes the received power can be determined whilesuppressing the co-channel interference. This allows to improve andensure the communication quality under various spatial correlationconditions and hence to increase system capacity by the spatial divisionmultiplexing transmission. In addition, the ZF beam, which can becalculated in a smaller calculation amount than the MMSE beam, canreduce circuit size and the cost of the terminals.

Wireless base station device 1 may have the function of performingspatial division multiplexing transmission using transmit weightgeneration sections 6-1 to 6-n; beam selection section 7 and selectedtransmit weight information as the transmit weight. Transmit weightgeneration sections 6-1 to 6-n generate pieces of transmit weightinformation according to different algorithms. The sets of transmitweight information are used for wireless base station device 1 toperform spatial division multiplexing transmission with terminals 2-1 to2-s having one or more receiving unit antennas based on the channelinformation on terminals 2-1 to 2-s. Beam selection section 7 selects atransmit weight generation section 6 having a previously specifiedalgorithm, based on the channel information. Transmit beam formationsection 9 forms the transmit beams using the selected transmit weightinformation as the transmit weight. As a result, it becomes possible toimprove and ensure the communication quality under various spatialcorrelation conditions and hence to increase system capacity by thespatial division multiplexing transmission.

One of transmit weight generation sections 6-1 to 6-n may have thefunction of generating transmit weight information used to formeigenvector beams to be transmitted to terminals 2. This allows to use atransmit weight which can improve the reception quality of apredetermined terminal 2 at the time of spatial division multiplexingtransmission to terminals 2-1 to 2-s without a restriction to reduce theinterference to other terminals 2. The transmit weight is usedparticularly when the channel correlation between the terminals is low,depending on various spatial correlation conditions detected from thechannel information.

One of transmit weight generation sections 6-1 to 6-n may have thefunction of generating transmit weight information which causes littleor no interference to terminals 2 other than a predetermined terminal 2.This allows to use a transmit weight which can improve the receptionquality of a predetermined terminal 2 at the time of spatial divisionmultiplexing transmission to terminals 24 to 2-s with a restriction tominimize the interference to other terminals 2. The transmit weight isused particularly when the channel correlation between the terminals iscomparatively high, depending on various spatial correlation conditionsdetected from the channel information.

One of transmit weight generation sections 6-1 to 6-n may have thefunction of generating transmit weight information which causes littleor no interference to terminals 2 other than a predetermined terminal 2on the assumption that the predetermined terminal 2 performs receptionusing maximum ratio combining. This allows reducing the number ofrestrictions to minimize the interference to terminals 2 other than apredetermined terminal 2 at the time of spatial division multiplexingtransmission to terminals 2-1 to 2-s. The number of restrictions can bereduced when the channel correlation between the terminals iscomparatively high and the other terminals 2 each have a plurality ofreceiving unit antennas 20-1 to 20-m, depending on various spatialcorrelation conditions detected from the channel information. This makesit possible to use a transmit weight which can improve the receptionquality to a predetermined terminal 2.

One of transmit weight generation sections 6-1 to 6-n may have thefunction of generating transmit weight information used to form atransmit weight vector whose components are all zero. This allows to usea transmit weight which does not perform transmission to other terminals2 at the time of spatial division multiplexing transmission to terminals2-1 to 2-s. The transmit weight can be used particularly when thechannel correlation between the terminals is high depending on variousspatial correlation conditions detected from the channel information.

One of transmit weight generation sections 6-1 to 6-n may have thefunction of generating transmit weight information used to form apreviously fixed transmit weight vector. This allows to selectively varythe previously fixed transmit weight at the time of spatial divisionmultiplexing transmission to terminals 2-1 to 2-s, depending on variousspatial correlation conditions detected from the channel information. Asa result, it becomes possible to improve and ensure the communicationquality under various spatial correlation conditions and hence toincrease system capacity by the spatial division multiplexingtransmission.

Wireless base station device 1 may have the function of performingspatial division multiplexing transmission by inserting a known signalsequence into each spatial division multiplexing transmitted signalwhile using a transmit weight vector formed from the selected transmitweight information data. This allows to selectively vary the transmitweight generation algorithm at the time of spatial division multiplexingtransmission to terminals 2-1 to 2-s, depending on various spatialcorrelation conditions detected from the channel information. This alsoallows terminal 2 to separately receive a spatially multiplexed signalusing the known signal sequence inserted into each transmitted signal,even when the channel information includes an error. As a result, itbecomes possible to improve and ensure the communication quality undervarious spatial correlation conditions and hence to increase systemcapacity by the spatial division multiplexing transmission.

Terminals 2 may have the function of generating a reception weight,which is used to perform channel estimation, to separate a desiredsignal from the spatial division multiplexing signal, and to output itbased on the known signal sequence provided to eachspatially-multiplexed transmitted signal. This allows terminal 2 toseparately receive a spatially multiplexed signal at the time of spatialdivision multiplexing transmission to terminals 2-1 to 2-s, using aknown signal sequence provided to each transmission signal.

Consequently, when wireless base station device 1 generates a transmitweight based on the channel information containing an error, terminals 2can separately receive a spatially multiplexed signal using a knownsignal sequence provided to each transmission signal. As a result, itbecomes possible to improve and ensure the communication quality undervarious spatial correlation conditions and hence to increase systemcapacity by the spatial division multiplexing transmission.

Channel estimation section 222 and spatial division demultiplexingsection 223 may have the function of generating a maximum ratiocombining reception weight as a reception weight, based on the valueobtained by channel estimation in channel estimation section 222. Thisallows terminal 2 to separately receive a spatially multiplexed signalat the time of spatial division multiplexing transmission to terminals2-1 to 2-s, using a known signal sequence provided to each transmissionsignal.

Consequently, when wireless base station device 1 generates a transmitweight based on the channel information containing an error, terminals 2can separately receive a spatially multiplexed signal in such a manneras to have the highest received power using a known signal sequenceprovided to each transmission signal. As a result, it becomes possibleto improve and ensure the communication quality under various spatialcorrelation conditions and hence to increase system capacity by thespatial division multiplexing transmission.

Channel estimation section 222 and spatial division demultiplexingsection 223 may have the function of generating aminimum-mean-square-error weight as a reception weight based on thevalue obtained by channel estimation in channel estimation section 222.This allows terminal 2 to separately receive a spatially multiplexedsignal at the time of spatial division multiplexing transmission toterminals 2-1 to 2-s, using a known signal sequence provided to eachtransmission signal.

Consequently, when wireless base station device 1 generates a transmitweight based on the channel information containing an error, terminals 2can separately receive a spatially multiplexed signal in such a mannerthat the desired signal has the highestdesired-signal-received-power-to-interference-and-Noise-power ratio,using a known signal sequence provided to each transmission signal. As aresult, it becomes possible to improve and ensure the communicationquality under various spatial correlation conditions and hence toincrease system capacity by the spatial division multiplexingtransmission.

Channel estimation section 222 and spatial division demultiplexingsection 223 may have the function of generating a left singular vectorcorresponding to a maximum singular value as a reception weight. Themaximum singular value is obtained by performing a singular valuedecomposition of a channel estimation matrix obtained by channelestimation based on a known signal sequence inserted into eachspatially-multiplexed transmitted signal. The reception weight is usedto separate a desired signal from the spatial division multiplexingsignal and to output it. This allows to terminal 2 to separately receivea spatially multiplexed signal using the known signal sequence insertedinto each transmission signal on the terminal side at the time ofspatial division multiplexing transmission to terminals 2-1 to 2-s.

Consequently, particularly when a transmit weight used to improve thereception quality of a predetermined terminal 2 is used with arestriction to minimize the interference to the other terminals 2, theco-channel interference to the other terminals 2 can be reduced and thereceived power of the spatially multiplexed signal component can bemaximized. As a result, it becomes possible to improve and ensure thecommunication quality and hence to increase system capacity by thespatial division multiplexing transmission.

The wireless communication method of the present invention may have thefollowing two steps. One step is to extract channel information betweenterminals 2 and wireless base station device 1 from the signals receivedfrom terminals 2, and to determine a spatial correlation coefficientbetween the terminals with which wireless base station device 1 performsspatial division multiplexing transmission, based on the extractedchannel information.

The other step is to select one of the following first to third typesthat provides the best communication quality according to the spatialcorrelation coefficient obtained by the former step, based on apredetermined selection process. The first type generates transmitweights according to an algorithm to generate a transmit weight whichimprove the reception quality of a predetermined terminal with arestriction to minimize the interference to other terminals 2. Thesecond type generates transmit weights according to an algorithm togenerate a transmit weight which improves the reception quality of apredetermined terminal without a restriction to reduce the interferenceto other terminals 2. The third type generates a transmit weightaccording to an algorithm to generate a single transmit weight. Thewireless communication method with these two steps can use a specificrelationship existing between the three different algorithms fortransmit weight generation about the spatial correlationcoefficient-to-communication quality characteristics. Thecharacteristics are divided into a plurality of regions according to thespecific relationship, and it is designed that an algorithm providingthe best communication quality is selected in each of the regionsautomatically from among the three algorithms. This eliminates the needto select an optimum type every time the spatial correlation coefficientis calculated, thereby selecting a transmit weight generation algorithmoptimum for the spatial correlation conditions of the terminals. As aresult, spatial division multiplexing transmission can be robust to thespatial correlation conditions between the terminals. This simplifiesthe allocation process of the terminals to be connected by spatialdivision multiplexing, thereby reducing processing time, and alsoincreases system capacity by spatial division multiplexing transmission.

Second Embodiment

Wireless base station device 100 of a second embodiment of the presentinvention is shown in FIG. 11.

Wireless base station device 100 differs from wireless base stationdevice 1 of the first embodiment in that there is provided selectorswitch section 107-a instead of beam selection section 7 and there isfurther provided selector switch section 107-b between channelinformation acquisition section 4 and transmit weight generationsections 6-1 to 6-n. From a functional point of view, device 100 differsfrom device 1 in that channel information acquisition section 4 has notonly the conventional function of extracting channel information butalso the function of controlling selector switch sections so as toselect the optimum transmit weight generation section 6 based on theextracted channel information.

On the other hand, selector switch sections 107-a and 107-b areassociated with each other. For example, when selector switch section107-b selects transmit weight generation section 6-1, selector switchsection 107-a is connected to the output side of transmit weightgeneration section 6-1. Selector switch section 107-b is furtherassociated with the operation switches of the transmit weight generationsections 6. As soon as transmit weight generation sections 6 connectedthereto are powered on, selector switch section 107-b receives channelinformation. This operation extracts channel information, selects theoptimum transmit weight generation section 6, and obtains transmitweight information outputted therefrom.

This allows operating only the selected transmit weight generationsection 6 so that wireless base station device 100 can have a reducedpower consumption in addition to the advantage of the first embodimentof the present invention. Furthermore, in the case where the transmitweights in transmit weight generation sections 6 are calculated usingthe common CPU, the selected transmit weight generation section 6occupies the CPU, thereby improving arithmetic processing capability.This improves the throughput of the total system.

As described hereinbefore, in the present second embodiment, selectorswitch sections 107-a and 107-b are provided on both sides of transmitweight generation sections 6-1 to 6-n. Selector switch sections 107-aand 107-b select an arbitrary one of transmit weight generation sections6-1 to 6-n which generate transmit weights used to perform spatialdivision multiplexing transmission with terminals 2-1 to 2-s with whichwireless base station device 100 performs spatial division multiplexingtransmission, based on the channel information on terminals 2-1 to 2-s.As a result, it becomes possible to improve and ensure the communicationquality under various spatial correlation conditions and hence toincrease system capacity by the spatial division multiplexingtransmission.

It is also possible to select a transmit weight generation algorithmthat is optimum to the spatial correlation conditions between theterminals. This achieves spatial division multiplexing transmissionrobust to the spatial correlation conditions between the terminals,thereby simplifying the conventional allocation process based on thespatial correlation coefficient. Furthermore, wireless base stationdevice 100 can have a reduced power consumption, and the arithmeticprocessing capability can be improved, thereby improving the throughputof the total system. In addition, wireless base station device 100 canbe simplified and the processing time required to control the spatialdivision multiplexing transmission can be reduced.

Transmit power determination section 8 may have the function ofdetermining the transmit powers of the spatial division multiplexingsignals to be transmitted to terminals 2-1 to 2-s based on the selectedtransmit weight information. This allows to select an optimum one of thedifferent transmit weight generation algorithms and to generate atransmit weight that is optimum for the spatial correlation conditionsdetected from the channel information according to the selected transmitweight generation algorithm at the time of spatial division multiplexingtransmission to terminals 2-1 to 2-s. The structure also allows tocontrol the powers required to transmit signals using these transmitweights.

This makes it possible to perform transmission using signal power tosatisfy predetermined communication quality, that is, without using morethan necessary transmit power, thereby reducing co-channel interferenceand increasing system capacity.

One of transmit weight generation sections 6-1 to 6-n may have thefunction of generating transmit weight information used to formeigenvector beams to be transmitted to terminals 2-1 to 2-s. This allowsto use a transmit weight which can improve the reception quality of apredetermined terminal 2 at the time of spatial division multiplexingtransmission to terminals 2-1 to 2-s without a restriction to reduce theinterference to other terminals 2. The transmit weight can be usedparticularly when the channel correlation between the terminals is low,depending on various spatial correlation conditions detected from thechannel information.

One of transmit weight generation sections 6-1 to 6-n may have thefunction of generating transmit weight information which causes littleor no interference to terminals 2 other than a predetermined terminal 2.This allows to use a transmit weight which can improve the receptionquality of a predetermined terminal 2 at the time of spatial divisionmultiplexing transmission to terminals 2-1 to 2-s with a restriction tominimize the interference to other terminals 2. The transmit weight canbe used particularly when the channel correlation between the terminalsis comparatively high, depending on various spatial correlationconditions detected from the channel information.

One of transmit weight generation sections 6-1 to 6-n may have thefunction of generating transmit weight information which causes littleor no interference to terminals 2 other than a predetermined terminal 2on the assumption that the predetermined terminal 2 performs receptionusing maximum ratio combining. This allows to reduce the number ofrestrictions to minimize the interference to terminals 2 other than apredetermined terminal 2 at the time of spatial division multiplexingtransmission to terminals 2-1 to 2-s, when the channel correlationbetween the terminals is comparatively high and the other terminals 2each have a plurality of receiving unit antennas 20-1 to 20-m, dependingon various spatial correlation conditions detected from the channelinformation. This makes it possible to use a transmit weight which canimprove the reception quality to a predetermined terminal 2.

One of transmit weight generation sections 6-1 to 6-n may have thefunction of generating transmit weight information used to form atransmit weight vector whose components are all zero. This allows to usea transmit weight which does not perform transmission to other terminals2 at the time of spatial division multiplexing transmission to terminals2-1 to 2-s. The transmit weight can be used particularly when thechannel correlation between the terminals is high depending on variousspatial correlation conditions detected from the channel information.

One of transmit weight generation sections 6-1 to 6-n may have thefunction of generating transmit weight information used to form apreviously fixed transmit weight vector. This allows to selectively varythe previously fixed transmit weight at the time of spatial divisionmultiplexing transmission to terminals 2-1 to 2-s, depending on variousspatial correlation conditions detected from the channel information. Asa result, it becomes possible to improve and ensure the communicationquality under various spatial correlation conditions and hence toincrease system capacity by the spatial division multiplexingtransmission.

Wireless base station device 100 may have the function of performingspatial division multiplexing transmission by inserting a known signalsequence into each spatially-multiplexed transmitted signal while usinga transmit weight vector formed from the selected transmit weightinformation data. This allows to selectively vary the transmit weightgeneration algorithm at the time of spatial division multiplexingtransmission to terminals 2-1 to 2-s, depending on various spatialcorrelation conditions detected from the channel information. This alsoallows terminal 2 to separately receive a spatially multiplexed signalusing the known signal sequence inserted into each transmission signal,even when the channel information includes an error. As a result, itbecomes possible to improve and ensure the communication quality undervarious spatial correlation conditions and hence to increase systemcapacity by the spatial division multiplexing transmission.

Third Embodiment

Wireless base station device 1-A and terminal 2-C of a third embodimentof the present invention are shown in FIG. 12 and FIG. 13, respectively.Wireless base station device 1-A of the present embodiment differs fromwireless base station device 1 of the first embodiment in that there areprovided separation algorithm acquisition section 400 and beam selectionsection 401. Separation algorithm information acquisition section 400acquires spatial division demultiplexing algorithm informationtransmitted from terminal 2-C. Beam selection section 401 selects one ofthe outputs of transmit weight generation sections 6-1 to 6-n based onthe spatial division demultiplexing algorithm information. Terminal 2-Cof the present embodiment differs from terminal 2-A of the firstembodiment in that terminal 2-C includes spatial division demultiplexingalgorithm storage section 300 and transmission section 212-A. Spatialdivision demultiplexing algorithm storage section 300 stores spatialdivision demultiplexing algorithm information used in spatial divisiondemultiplexing section 223 which terminal 2-C uses during reception.Transmission section 212-A applies appropriate data processing tospatial division demultiplexing algorithm information 301, which is theoutput information of spatial division demultiplexing algorithm storagesection 300 and converts it into a radio frequency signal. The followingdescription is focused on the operations of the elements added to ormodified from those in the first embodiment.

In FIG. 13, terminal 2-C of the present third embodiment having aplurality of antennas includes transmission unit 210 having transmittingunit antenna 216 and reception unit 220 having receiving unit antennas20-1 to 20-m.

Transmission unit 210 includes data input section 214 which receivesdata information that the terminal user is going to transmit; andtransmission section 212-A. Transmission section 212-A appliesappropriate data processing to channel estimation informationtransmitted from channel estimation section 222 and to spatial divisiondemultiplexing algorithm information 301. Spatial divisiondemultiplexing algorithm information 301 is the output information ofspatial division demultiplexing algorithm storage section 300 storingthe spatial division demultiplexing algorithm information used inspatial division demultiplexing section 223. Transmission section 212-Athen converts the information into radio frequency signals. The spatialdivision demultiplexing algorithm information includes spatial divisiondemultiplexing algorithms such as MMSE, ZF, MLD (Maximum LikelihoodDetection), SIC (Successive (or Serial)-Interference-Canceller), and PIC(Parallel-Interference-Canceller). The information can be transmittedusing a categorized table to transmit assigned classification numbers soas to reduce the amount of information to be transmitted. Alternatively,a table can be used which ranks the separation algorithms using aperformance indicator so as to categorize, for example, MMSE and ZF asclass 1; SIC and PIC as class 2; and MLD as class 3.

Reception unit 220 includes reception sections 221-1 to 221-m; channelestimation section 222; spatial division demultiplexing section 223;demodulation section 224; and data output section 225. Receptionsections 221-1 to 221-m, which correspond to receiving unit antennas20-1 to 20-m, respectively, convert radio frequency signals received byreceiving antennas 20-1 to 20-m into baseband signals. Channelestimation section 222 estimates channel response information of thepropagation paths from baseband signals in the downlink. Spatialdivision demultiplexing section 223 separates and extracts a desiredsignal from each of the spatial division multiplexing signals based onthe channel response information obtained in channel estimation section222. Demodulation section 224 restores transmission data sequences fromthe separately received desired signals. Data output section 225 eitheroutputs the restored reception data sequences to the other apparatus ornotifies the information to the terminal user.

Transmitting unit antenna 216 and receiving unit antenna 20-1 to 20-mare treated as different components; however, alternatively,transmitting unit antenna 216 can be integrated with one of receivingunit antennas 20-1 to 20-m.

The following is a description of the operations of wireless basestation device 1-A and terminal 2-C. Assuming that the channelinformation of the downlink has been estimated by terminals 2-1 to 2-s,the operation to provide this information to wireless base stationdevice 1-A is briefly described.

First, the channel information of a propagation path (unillustrated)estimated by channel estimation section 222 in transmission unit 210 ofterminal 2-C is transmitted to transmission section 212-A and thentransmitted to wireless base station device 1-A via a control channel ora broadcasting control channel. In other words, a control channel signalor a broadcasting control channel signal carrying the channelinformation is transmitted to transmitting unit antenna 216 and thenemitted therefrom to the propagation path (unillustrated) so as to betransmitted to wireless base station device 1-A.

The control channel or the broadcasting control channel is acommunication channel to exchange information of the efficient operationbetween wireless base station device 1-A and terminal 2-C and isdifferent from a communication channel to exchange information betweenthe user of terminal 2-C and wireless base station device 1-A.

The information that the user of terminal 2-C is going to transmit istransferred from data input section 214 to transmission section 212-Awhere the information is subjected to appropriate signal processing;converted into a radio frequency signal; and transmitted to wirelessbase station device 1-A via transmitting unit antenna 216.

Later, in wireless base station device 1-A, channel informationacquisition section 4 extracts the channel information contained in thecontrol channel signal or the broadcasting control channel signaltransmitted from each of terminals 2-1 to 2-s to wireless base stationantennas 11-1 to 11-s. Terminals 2-1 to 2-s have the structure ofterminal 2-C. Channel information acquisition section 4 then outputs theextracted channel information to transmit weight determination section5.

The following is a brief description of the operation of spatialdivision multiplexing transmission by multiplying each of the signals tobe transmitted to terminals 2-1 to 2-s by an appropriate transmitweight. Terminals 2-1 to 2-s are to be connected by spatial divisionmultiplexing (allocated) based on the channel information of thedownlink and the spatial division demultiplexing algorithm informationwhich have been notified to wireless base station device 1-A.

First, in wireless base station device 1-A, channel informationacquisition section 4 extracts the channel information contained in thecontrol channel signal or the broadcasting control channel signaltransmitted to wireless base station antennas 11-1 to 11-s from each ofterminals 2-1 to 2-s to be connected by spatial division multiplexing(allocated). Channel information acquisition section 4 then outputs theextracted channel information to transmit weight determination section5. The channel information thus extracted is the channel information ofthe downlink from wireless base station device 1-A to terminals 2-1 to2-s. Furthermore, separation algorithm information acquisition section400 extracts the spatial division demultiplexing algorithm informationcontained in the control channel signal or the broadcasting controlchannel signal transmitted to wireless base station antennas 11-1 to11-s from each of terminals 2-1 to 2-s to be connected by spatialdivision multiplexing (allocated). Separation algorithm informationacquisition section 400 then outputs the extracted spatial divisiondemultiplexing algorithm information to transmit weight determinationsection 5.

Next, in transmit weight determination section 5, transmit weightgeneration sections 6-1 to 6-n, which have different transmit weightgeneration algorithms, generate pieces of transmit weight generationinformation. This allows transmitting an optimum signal to terminals 2-1to 2-s to be connected by spatial division multiplexing in accordancewith the correlation conditions between terminals 2-1 to 2-s. Then, beamselection section 401 selects the transmit weight information thatmaximizes a predetermined criterion from among the pieces of transmitweight generation information generated by first to n-th transmit weightgeneration sections 6-1 to 6-n. Beam selection section 401 then outputsthe selected information to transmit power determination section 8 andtransmit beam formation section 9.

Next, transmit power determination section 8 determines a powerdistribution factor used to determine the transmit power for eachspatial division multiplexing stream, based on the received transmitweight information.

On the other hand, transmission signal generation sections 3-1 to 3-sgenerate signals to be transmitted to terminals 2-1 to 2-s to beconnected by spatial division multiplexing (preferably allocated). Thesignals to be transmitted to terminals 2-1 to 2-s (hereinafter,“transmission data sequences”) are outputted after being subjected toappropriate signal processing.

Power factor multipliers 10-1 to 10-s multiply the signal output of eachof transmission signal generation sections 3-1 to 3-s by thecorresponding one of the power distribution factors determined bytransmit power determination section 8.

Transmit beam formation section 9 generates baseband symbol data bymultiplying each of transmission data frame sequence signals by atransmit weight used to form a predetermined (selected) beam, based onthe transmit weight information from beam selection section 401. Thetransmission data frame sequence signals have been obtained by themultiplication between the signal outputs and the power distributionfactors. After this, in transmit beam formation section 9, digital data,which are the baseband symbol data, are digital-analog converted by anunillustrated digital-analog converter, filtered by an unillustratedband limiting filter, and converted into carrier frequencies by anunillustrated frequency converter, thereby being outputted as radiofrequency signals. Wireless base station antennas 11-1 to 11-s emit thereceived radio frequency signals to unillustrated propagation paths(space) so as to transmit these signals to terminals 2-1 to 2-s to beconnected by spatial division multiplexing.

How terminals 2-1 to 2-s receive the spatially multiplexed signalstransmitted from wireless base station device 1 is omitted because it isidentical to that of the first embodiment.

Concerning the aforementioned items [1] to [3], no detailed descriptionis given to [1] Transmit weight generation algorithms implemented intransmit weight generation sections 6-1 to 6-n and to [3] How todetermine the transmit power distribution factor because it is identicalto that of the first embodiment. The following description is focused on[2] How beam selection section 401 selects transmit weight information,which is different from that of the first embodiment.

A detailed description on [2] How beam selection section 401 selectstransmit weight information

How beam selection section 401 selects transmit weight information isdescribed in detail as follows. Beam selection section 401 selects atransmit weight information that maximizes a predetermined criterionfrom among pieces of transmit weight information generated by first ton-th transmit weight generation sections 6-1 to 6-n. The criterion isdetermined by calculating a predicted value of physical quantity basedon the output of separation algorithm information acquisition section400. The physical quantity indicates signal quality such as thesignal-to-noise power ratio (SNR) or the signal-to-interference andnoise power ratio (SINR) received by terminal 2-C. This is the pointwhere beam selection section 401 is different from beam selectionsection 7 of the first embodiment.

More specifically, in the first embodiment, when terminal 2-k has aplurality of antennas, SINR estimation is performed using Equation 17 onthe assumption that the directivity is formed using reception weightR(k). In contrast, in the present embodiment, reception weight R(k) isgenerated using channel information H(k) on k-th terminal 2-k based onspatial division demultiplexing algorithm information of terminal 2-k,which is the output of separation algorithm information acquisitionsection 400. Reception weight R(k) represents a column vector havingNr(k) elements the same number as the number of receiving unit antennasof terminal 2-k. In Equation 17, the subscript “n” represents the numberof user terminals, that is, the total number of terminals 2 to beconnected by spatial division multiplexing, which corresponds toterminals 2-1 to 2-s in the present embodiment. The spatial divisiondemultiplexing algorithm information can be MMSE algorithm, ZFalgorithm, or eigenvector beam reception algorithm when there is aninterference component and can be a maximum ratio combining receptionweight when there is no need to consider an interference component.

Through the aforementioned calculations, SINRn(k) of each user iscalculated using Wn(k) expressed by Equation 17 as a variable. SINRn(k)is calculated for the outputs of all of the first to n-th transmitweight generation sections. Then, beam selection section 401 selectstransmit weight Ws(k) where k=1 to Ns. Transmit weight Ws(k) is theoutput information of s-th transmit weight generation section 6-s whichgenerates the transmit weight making the total SINRn(k) of all userslargest.

As described hereinbefore, in the third embodiment of the presentinvention, predicted SINR estimation is performed using the spatialdivision demultiplexing algorithm information transmitted from aterminal. This allows the predicted SINR evaluated value to approachcloser to the SINR actually received by the terminals. Thus, suchpredicted SINR can be used to select an optimum transmit weight, therebyimproving the communication quality of terminals 2 and increasing thecommunication system capacity.

The predicted SINR is also used to determine a transmit powerdistribution factor. This allows the predicted SINR evaluated value toapproach closer to the SINR actually received by the terminals, therebyperforming an optimum power distribution. Such transmit power controlensures that the communications quality of terminal 2 for communicationis at a sufficient level, and eliminates the need to increase thetransmit power more than necessary. As a result, the present embodimentcan be applied to a cellular system to reduce the inter-cellinterference and increase the communication system capacity.

Fourth Embodiment

Wireless base station device 1-B and terminal 2-D of a fourth embodimentof the present invention are shown in FIG. 14 and FIG. 15, respectively.Wireless base station device 1-B differs from wireless base stationdevice 1 of the first embodiment in that there are provided other-cellinterference information acquisition section 410 and beam selectionsection 411. Other-cell interference information acquisition section 410acquires other-cell interference information transmitted from terminal2-D. Beam selection section 411 selects one of the outputs of transmitweight generation sections 6-1 to 6-n based on the acquired other-cellinterference information.

Terminal 2-D of the present embodiment differs from terminal 2-A of thefirst embodiment in that there are provided other-cell interferencedetection section 302 and transmission section 212-B. Other-cellinterference detection section 302 measures the conditions ofinterference that terminal 2-D receives from other cells duringreception. Transmission section 212-B provides appropriate dataprocessing to other-cell interference information 310, which is outputinformation thereof, and converts it into radio frequency signal. Thefollowing description is focused on the operations of the elements addedto or modified from those in the first embodiment.

In FIG. 15, terminal 2-D of the fourth embodiment having a plurality ofantennas includes transmission unit 210 having transmitting unit antenna216 and reception unit 220 having receiving unit antennas 20-1 to 20-m.

Transmission unit 210 includes data input section 214 and transmissionsection 212-B. Data input section 214 receives data information that theterminal user is going to transmit. Transmission section 212-B performsappropriate data processing to channel estimation informationtransmitted from channel estimation section 222 and other-cellinterference information outputted from other-cell interferencedetection section 302. Transmission section 212-B then converts theinformation to a radio frequency signal.

Reception unit 220 includes reception sections 221-1 to 221-m; channelestimation section 222; spatial division demultiplexing section 223;demodulation section 224; and data output section 225. Receptionsections 221-1 to 221-m correspond to receiving unit antennas 20-1 to20-m, respectively, and convert the radio frequency signals received byreceiving unit antennas 20-1 to 20-m into baseband signals. Channelestimation section 222 estimates channel response information ofpropagation paths of the downlink from the baseband signals. Spatialdivision demultiplexing section 223 separates and extracts desiredsignals from spatial division multiplexing signals based on the channelresponse information obtained by channel estimation section 222.Demodulation section 224 restores the transmission data sequences fromthe separated desired signals. Data output section 225 either outputsthe restored reception data sequences to another apparatus or providesthe information to the terminal user.

Note that transmitting unit antenna 216 and receiving unit antennas 20-1to 20-m are treated as different components; however, alternatively,transmitting unit antenna 216 can be integrated with one of receivingunit antennas 20-1 to 20-m.

The following is a description of wireless base station device 1-B andterminal 2-D. Assuming that the channel information of the downlink hasbeen estimated by terminals 2-1 to 2-s, the operation to provide thisinformation to wireless base station device 1-B is briefly described.

First, the channel information of a propagation path (unillustrated)estimated by channel estimation section 222 in transmission unit 210 ofterminal 2-D is transmitted to transmission section 212-B and thentransmitted to wireless base station device 1-B via a control channel ora broadcasting control channel. In other words, a control channel signalor a broadcasting control channel signal carrying the channelinformation is transmitted to transmitting unit antenna 216 and thenemitted therefrom to the propagation path (unillustrated) so as to betransmitted to wireless base station device 1-B.

The control channel or the broadcasting control channel is acommunication channel to exchange information of the efficient operationbetween wireless base station device 1-B and terminal 2-D and isdifferent from a communication channel to exchange information betweenthe user of terminal 2D and wireless base station device 1-B.

The information that the user of terminal 2-D is going to transmit istransferred from data input section 214 to transmission section 212-Bwhere the information is subjected to appropriate signal processing;converted into a radio frequency signal; and transmitted to wirelessbase station device 1-B via transmitting unit antenna 216.

Later, in wireless base station device 1-B, channel informationacquisition section 4 extracts the channel information contained in thecontrol channel signal or the broadcasting control channel signaltransmitted from each of terminals 2-1 to 2-s to wireless base stationantennas 11-1 to 11-s. Terminals 2-1 to 2-s have the structure ofterminal 2-D. Channel information acquisition section 4 then outputs theextracted channel information to transmit weight determination section5.

The following is a brief description of the operation of spatialdivision multiplexing transmission by multiplying each of the signals tobe transmitted to terminals 2-1 to 2-s by an appropriate transmitweight. Terminals 2-1 to 2-s are to be connected by spatial divisionmultiplexing (allocated) based on the channel information of thedownlink which has been notified to wireless base station device 1.

First, in wireless base station device 1-B, channel informationacquisition section 4 extracts the channel information contained in thecontrol channel signal or the broadcasting control channel signaltransmitted to wireless base station antennas 11-1 to 11-s from each ofterminals 2-1 to 2-s to be connected by spatial division multiplexing(allocated). Channel information acquisition section 4 then outputs theextracted channel information to transmit weight determination section5. The channel information thus extracted is the channel information ofthe downlink from wireless base station device 1-B to terminals 2-1 to2-s. Furthermore, other-cell interference information acquisitionsection 410 extracts the other-cell interference information containedin the control channel signal or the broadcasting control channel signaltransmitted to wireless base station antennas 11-1 to 11-s from each ofterminals 2-1 to 2-s to be connected by spatial division multiplexing(allocated). Other-cell interference information acquisition section 410then outputs the extracted other-cell interference information totransmit weight determination section 5.

Next, in transmit weight determination section 5, transmit weightgeneration sections 6-1 to 6-n, which have different transmit weightgeneration algorithms, generate different sets of transmit weightgeneration information. This allows transmitting an optimum signal toterminals 2-1 to 2-s to be connected by spatial division multiplexing inaccordance with the correlation conditions between terminals 2-1 to 2-s.

Then, beam selection section 411 selects the transmit weight informationthat maximizes a predetermined criterion from among the pieces oftransmit weight generation information generated by first to n-thtransmit weight generation sections 6-1 to 6-n. Beam selection section411 then outputs the selected information to transmit powerdetermination section 8 and to transmit beam formation section 9.

Next, transmit power determination section 8 determines a powerdistribution factor used to determine the transmit power for eachspatial division multiplexing stream, based on the received transmitweight information.

On the other hand, transmission signal generation sections 3-1 to 3-sgenerate signals to be transmitted to terminals 2-1 to 2-s to beconnected by spatial division multiplexing (preferably allocated). Thesignals to be transmitted to terminals 2-1 to 2-s (hereinafter,“transmission data sequences”) are outputted after being subjected toappropriate signal processing.

Power factor multipliers 10-1 to 10-s multiply the signal output of eachof transmission signal generation sections 3-1 to 3-s by thecorresponding one of the power distribution factors determined bytransmit power determination section 8. Transmit beam formation section9 generates baseband symbol data by multiplying each of transmissiondata frame sequence signals by a transmit weight used to form apredetermined or selected beam, based on the transmit weight informationfrom beam selection section 411. The transmission data frame sequencesignals have been obtained by the multiplication between the signaloutputs and the power distribution factors. After this, in transmit beamformation section 9, digital data, which are the baseband symbol data,are digital-analog converted by an unillustrated digital-analogconverter, filtered by an unillustrated band limiting filter, andconverted into carrier frequencies by an unillustrated frequencyconverter, thereby being outputted as radio frequency signals.

Wireless base station antennas 11-1 to 11-s emit the received radiofrequency signals to unillustrated propagation paths (space) so as totransmit these signals to terminals 2-1 to 2-s to be connected byspatial division multiplexing.

How terminals 2-1 to 2-s receive the spatially multiplexed signalstransmitted from wireless base station device 1-B is omitted because itis identical to that of the first embodiment.

Concerning the aforementioned items [1] to [3], no detailed descriptionis given to [1] Transmit weight generation algorithms implemented intransmit weight generation sections 6-1 to 6-n and to [3] How todetermine the transmit power distribution factor because it is identicalto that of the first embodiment. The following description is focused on[2] How beam selection section 411 selects transmit weight information,which is different from that of the first embodiment.

A detailed description on [2] How beam selection section 411 selectstransmit weight information

How beam selection section 411 selects transmit weight information isdescribed in detail as follows.

Beam selection section 411 selects a transmit weight information thatmaximizes a predetermined criterion from among pieces of transmit weightinformation generated by first to n-th transmit weight generationsections 6-1 to 6-n. The criterion is determined by calculating apredicted value of physical quantity based on the output of other-cellinterference information acquisition section 410. The physical quantityindicates signal quality such as the signal-to-noise power ratio (SNR)or the signal-to-interference and noise power ratio (SINR) received byterminal 2-D. This is the point where beam selection section 411 isdifferent from beam selection section 7 of the first embodiment.

More specifically, in the first embodiment, when there are pieces ofchannel information H(k) and terminal 2-k has a plurality of antennas,SINR estimation is performed using Equation 17 on the assumption thatthe directivity is formed using reception weight R(k). In contrast, inthe present embodiment, SINR estimation is performed using Equation 28including other-cell interference information F(k) of terminal 2-k,which is the output of other-cell interference information acquisitionsection 410.

$\begin{matrix}{{{SINR}_{n}(k)} = \frac{{{{R(k)}{H(k)}{W_{n}(k)}}}^{2}}{{\sum\limits_{{j = 1},{j \neq k}}^{Ns}{{{R(k)}{H(k)}{W_{n}(j)}}}^{2}} + {\sigma^{2}{{R(k)}}^{2}} + {F(K)}}} & {{Equation}\mspace{14mu} 28}\end{matrix}$

Reception weight R(k) represents a column vector having Nr(k) elementsthe same number as the number of receiving unit antennas of terminal2-k. In Equation 28, the subscript “n” represents the number of userterminals, that is, the total number of terminals 2 to be connected byspatial division multiplexing, which corresponds to terminals 2-1 to 2-sin the present embodiment. The spatial division demultiplexing algorithminformation can be MMSE algorithm, ZF algorithm, or eigenvector beamreception algorithm when there is an interference component and can be amaximum ratio combining reception weight when there is no need toconsider an interference component.

Through the aforementioned calculations, SINRn(k) of each user iscalculated using Wn(k) expressed by Equation 28 as a variable. SINRn(k)is calculated for the outputs of all of the first to n-th transmitweight generation sections. Then, beam selection section 411 selectstransmit weight Ws(k) where k=1 to Ns. Transmit weight Ws(k) is theoutput information of s-th transmit weight generation section 6-s whichgenerates the transmit weight making the total SINRn(k) of all userslargest.

As described hereinbefore in the fourth embodiment of the presentinvention, predicted SINR estimation is performed by using theother-cell interference information transmitted from terminal 2-D. Thisenables a predicted SINR reflecting the conditions of interferencecaused by other cells to be calculated only by the channel information,thereby allowing the predicted SINR evaluated value to approach closerto the SINR actually received by the terminals. Thus, such a predictedSINR can be used to select a transmit weight, making it possible toselect an optimum transmit weight, thereby improving the communicationquality of terminals 2 for communication and increasing thecommunication system capacity.

The predicted SINR is also used to determine a transmit powerdistribution factor. This allows the predicted SINR evaluated value toapproach closer to the SINR actually received by the terminals, therebyperforming an optimum power distribution. Such transmit power controlensures that the communication quality of terminals 2 for communicationis at a sufficient level, and eliminates the need to increase thetransmit power more than necessary. As a result, the present embodimentcan be applied to a cellular system to reduce the inter-cellinterference and increase the communication system capacity.

Terminal 2-D, which transmits the other-cell interference information towireless base station device 1-B in the present embodiment, can bereplaced by terminal 2-E having another structure as shown in FIG. 16.

Terminal 2-E shown in FIG. 16 differs from terminal 2-D in havingspatial division multiplexing transmission decision section 303 betweenother-cell interference detection section 302 and transmission section212-C of FIG. 15.

Spatial division multiplexing transmission decision section 303 comparesthe output value of other-cell interference detection section 302 withpredetermined threshold 304. When the other-cell interference is greaterthan the predetermined threshold, spatial division multiplexingtransmission decision section 303 decides that it is impossible toensure sufficient communication quality to perform spatial divisionmultiplexing transmission. Terminal 2-E then transmits spatial divisionmultiplexing transmission inhibition information as other-cellinterference information to wireless base station device 1-B. Thespatial division multiplexing transmission inhibition informationindicates that spatial division multiplexing transmission is notperformed. On the other hand, wireless base station device 1-B acquiresthe other-cell interference information. When the information containsthe spatial division multiplexing transmission inhibition information,wireless base station device 1-B performs communication in a mode notperforming spatial division multiplexing transmission.

The aforementioned structure allows terminals 2 to decide whetherspatial division multiplexing transmission is possible or not dependingon the other-cell interference conditions. More specifically, thethreshold to the other-cell interference is set generally depending onthe performance of reception system of the terminals, so that wirelessbase station device 1 cannot achieve a uniform judgment. Therefore, thecontrol of spatial division multiplexing transmission of wireless basestation device 1 can be better achieved based on the results judged byterminals 2. This ensures communication quality in an area that cannotignore interference caused by other cells, particularly by cell edges.

As described hereinbefore, in the present embodiment, it becomespossible to improve and ensure the communication quality under variousspatial correlation conditions and hence to increase system capacity bythe spatial division multiplexing transmission.

INDUSTRIAL APPLICABILITY

The wireless base station device and the terminal according to thepresent invention are useful in the field of wireless communicationusing spatial division multiplexing. This is because the wireless basestation device and the terminal have the function of selecting anoptimum weight information from among pieces of transmit weightinformation according to different algorithms depending on the spatialcorrelation characteristics of the terminals to be connected by spatialdivision multiplexing. This simplifies the wireless base station deviceand reduces the processing delay, thereby increasing the systemcapacity.

1. A wireless base station device comprising: a plurality of transmitweight generation sections generating pieces of transmit weightinformation according to different algorithms based on channelinformation for a plurality of terminals with which the wireless basestation device performs spatial division multiplexing transmission, thetransmit weight information being used to form transmit beams to betransmitted to the terminals; a beam selection section selecting one ofthe pieces of transmit weight information generated according to thealgorithms; and a transmit beam formation section forming the transmitbeams using the selected transmit weight information.
 2. The wirelessbase station device of claim 1, further comprising: a transmit powerdetermination section determining transmit power used for the spatialdivision multiplexing transmission based on the selected transmit weightinformation.
 3. The wireless base station device of claim 1, wherein thebeam selection section selects transmit weight information based oninformation showing a signal-to-interference and noise power ratio atthe terminals.
 4. The wireless base station device of claim 1, whereinthe beam selection section selects transmit weight information based oninformation showing a signal-to-interference and noise power ratio atthe terminals, the information including other-cell interferenceinformation notified from the terminals.
 5. The wireless base stationdevice of claim 1, wherein the beam selection section selects transmitweight information using a predicted reception weight when each of theterminals can receive using a plurality of antennas, the predictedreception weight representing a prediction of a reception weight of theterminals.
 6. The wireless base station device of claim 5, wherein thepredicted reception weight is a weight used to form a maximum ratiocombining reception beam.
 7. The wireless base station device of claim5, wherein the predicted reception weight is a left singular vectorobtained by performing a singular value decomposition of a channelmatrix.
 8. The wireless base station device of claim 5, wherein thepredicted reception weight is a weight used to form aminimum-mean-square-error beam.
 9. The wireless base station device ofclaim 5, wherein the predicted reception weight is a weight used to forma zero forcing beam.
 10. The wireless base station device of claim 5,wherein the predicted reception weight is a weight to be formed based ona spatial division demultiplexing algorithm notified from the terminals.11. The wireless base station device of claim 5, wherein the predictedreception weight is a weight to inhibit spatial division multiplexingtransmission when a decision notified from the terminals indicatesinhibition of spatial division multiplexing transmission.
 12. Thewireless base station device of claim 1, wherein the beam selectionsection selects a transmit weight generation section having a previouslyspecified algorithm based on the channel information.
 13. The wirelessbase station device of claim 1, wherein one of the plurality of transmitweight generation sections generates transmit weight information used toform eigenvector beams for the terminals.
 14. The wireless base stationdevice of claim 1, wherein one of the plurality of transmit weightgeneration sections generates transmit weight information causing littleor no interference to terminals other than a predetermined terminal. 15.The wireless base station device of claim 1, wherein one of theplurality of transmit weight generation sections generates transmitweight information causing little or no interference to terminals otherthan a predetermined terminal on an assumption that a predeterminedterminal performs reception using maximum ratio combining.
 16. Thewireless base station device of claim 1, wherein one of the plurality oftransmit weight generation sections generates transmit weightinformation used to form a transmit weight vector whose components areall zero.
 17. The wireless base station device of claim 1, wherein oneof the plurality of transmit weight generation sections generatestransmit weight information used to form a previously fixed transmitweight vector.
 18. The wireless base station device of claim 1, whereinthe transmit beam formation section performs spatial divisionmultiplexing transmission while a known signal sequence is inserted intoeach spatially-multiplexed transmitted signal using a transmit weightvector formed using the selected transmit weight information.